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Practice Questions

Practice100 questions

Question 1

Find the Smallest Number in an Array

Problem

Given an array of N integers, find and return the smallest element.

Example:

Input: arr = [5, 3, 7, 2, 8]
Output: 2

Code

Java

import java.util.Scanner;
public class SmallestElement {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int min = arr[0];
        for (int i = 1; i < n; i++) {
            if (arr[i] < min) min = arr[i];
        }
        System.out.println(min);
    }
}

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    int arr[n];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);
    int min = arr[0];
    for (int i = 1; i < n; i++) {
        if (arr[i] < min) min = arr[i];
    }
    printf("%d\n", min);
    return 0;
}

Python

n = int(input())
arr = list(map(int, input().split()))
print(min(arr))

Time: O(N)Space: O(1)

Question 2

Find the Largest Number in an Array

Problem

Given an array of N integers, find and return the largest element.

Example:

Input: arr = [5, 3, 7, 2, 8]
Output: 8

Code

Java

import java.util.Scanner;
public class LargestElement {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int max = arr[0];
        for (int i = 1; i < n; i++) {
            if (arr[i] > max) max = arr[i];
        }
        System.out.println(max);
    }
}

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    int arr[n];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);
    int max = arr[0];
    for (int i = 1; i < n; i++) {
        if (arr[i] > max) max = arr[i];
    }
    printf("%d\n", max);
    return 0;
}

Python

n = int(input())
arr = list(map(int, input().split()))
print(max(arr))

Time: O(N)Space: O(1)

Question 3

Second Smallest and Second Largest Element in an Array

Problem

Given an array of N integers, find the second smallest and second largest elements.

Example:

Input: arr = [5, 3, 7, 2, 8]
Output: Second Smallest = 3, Second Largest = 7

Code

Java

import java.util.Scanner;
public class SecondSmallestLargest {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int min1 = Integer.MAX_VALUE, min2 = Integer.MAX_VALUE;
        int max1 = Integer.MIN_VALUE, max2 = Integer.MIN_VALUE;
        for (int x : arr) {
            if (x < min1) { min2 = min1; min1 = x; }
            else if (x < min2 && x != min1) min2 = x;
            if (x > max1) { max2 = max1; max1 = x; }
            else if (x > max2 && x != max1) max2 = x;
        }
        System.out.println("Second Smallest = " + min2);
        System.out.println("Second Largest = " + max2);
    }
}

#include <stdio.h>
#include <limits.h>
int main() {
    int n;
    scanf("%d", &n);
    int arr[n];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);
    int min1 = INT_MAX, min2 = INT_MAX;
    int max1 = INT_MIN, max2 = INT_MIN;
    for (int i = 0; i < n; i++) {
        if (arr[i] < min1) { min2 = min1; min1 = arr[i]; }
        else if (arr[i] < min2 && arr[i] != min1) min2 = arr[i];
        if (arr[i] > max1) { max2 = max1; max1 = arr[i]; }
        else if (arr[i] > max2 && arr[i] != max1) max2 = arr[i];
    }
    printf("Second Smallest = %d\nSecond Largest = %d\n", min2, max2);
    return 0;
}

Python

n = int(input())
arr = list(map(int, input().split()))
unique = sorted(set(arr))
print("Second Smallest =", unique[1])
print("Second Largest =", unique[-2])

Time: O(N)Space: O(1)

Question 4

Reverse a Given Array

Problem

Given an array of N integers, reverse the array in-place.

Example:

Input: arr = [1, 2, 3, 4, 5]
Output: [5, 4, 3, 2, 1]

Code

Java

import java.util.Scanner;
public class ReverseArray {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        for (int i = 0; i < n / 2; i++) {
            int temp = arr[i];
            arr[i] = arr[n - 1 - i];
            arr[n - 1 - i] = temp;
        }
        for (int x : arr) System.out.print(x + " ");
    }
}

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    int arr[n];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);
    for (int i = 0; i < n / 2; i++) {
        int temp = arr[i];
        arr[i] = arr[n - 1 - i];
        arr[n - 1 - i] = temp;
    }
    for (int i = 0; i < n; i++) printf("%d ", arr[i]);
    return 0;
}

Python

n = int(input())
arr = list(map(int, input().split()))
arr.reverse()
print(*arr)

Time: O(N)Space: O(1)

Question 5

Count Frequency of Each Element in an Array

Problem

Given an array of N integers, count and print the frequency of each distinct element.

Example:

Input: arr = [1, 2, 2, 3, 3, 3]
Output: 1->1, 2->2, 3->3

Code

Java

import java.util.*;
public class FrequencyCount {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        Map<Integer, Integer> freq = new LinkedHashMap<>();
        for (int x : arr) freq.put(x, freq.getOrDefault(x, 0) + 1);
        for (Map.Entry<Integer, Integer> e : freq.entrySet())
            System.out.println(e.getKey() + " -> " + e.getValue());
    }
}

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    int arr[n], visited[n];
    for (int i = 0; i < n; i++) { scanf("%d", &arr[i]); visited[i] = 0; }
    for (int i = 0; i < n; i++) {
        if (visited[i]) continue;
        int count = 1;
        for (int j = i + 1; j < n; j++) {
            if (arr[i] == arr[j]) { count++; visited[j] = 1; }
        }
        printf("%d -> %d\n", arr[i], count);
    }
    return 0;
}

Python

n = int(input())
arr = list(map(int, input().split()))
from collections import Counter
for k, v in Counter(arr).items():
    print(f"{k} -> {v}")

Time: O(N)Space: O(N)

Question 6

Rearrange Array in Increasing-Decreasing Order

Problem

Given an array, rearrange so first half is sorted ascending and second half sorted descending.

Example:

Input: arr = [5, 2, 8, 1, 9, 3]
Output: [1, 2, 3, 9, 8, 5]

Code

Java

import java.util.*;
public class RearrangeArray {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        Arrays.sort(arr);
        int mid = n / 2;
        for (int i = mid, j = n - 1; i < j; i++, j--) {
            int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp;
        }
        for (int x : arr) System.out.print(x + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
arr.sort()
mid = n // 2
result = arr[:mid] + arr[mid:][::-1]
print(*result)

Time: O(N log N)Space: O(1)

Question 7

Calculate Sum of the Elements of the Array

Problem

Given an array of N integers, calculate the sum of all elements.

Example:

Input: arr = [1, 2, 3, 4, 5]
Output: 15

Code

Java

import java.util.Scanner;
public class ArraySum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        for (int i = 0; i < n; i++) sum += sc.nextInt();
        System.out.println(sum);
    }
}

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    int arr[n];
    long long sum = 0;
    for (int i = 0; i < n; i++) { scanf("%d", &arr[i]); sum += arr[i]; }
    printf("%lld\n", sum);
    return 0;
}

Python

n = int(input())
arr = list(map(int, input().split()))
print(sum(arr))

Time: O(N)Space: O(1)

Question 8

Rotate Array by K Elements

Problem

Given an array and K, rotate left by K positions using the reversal algorithm.

Example:

Input: arr = [1, 2, 3, 4, 5, 6, 7], K = 2
Output: [3, 4, 5, 6, 7, 1, 2]

Code

Java

import java.util.Scanner;
public class RotateArray {
    static void reverse(int[] arr, int start, int end) {
        while (start < end) {
            int temp = arr[start]; arr[start] = arr[end]; arr[end] = temp;
            start++; end--;
        }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(), k = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        k = k % n;
        reverse(arr, 0, k - 1);
        reverse(arr, k, n - 1);
        reverse(arr, 0, n - 1);
        for (int x : arr) System.out.print(x + " ");
    }
}

Python

n, k = map(int, input().split())
arr = list(map(int, input().split()))
k = k % n
arr = arr[k:] + arr[:k]
print(*arr)

Time: O(N)Space: O(1)

Question 9

Average of All Elements in an Array

Problem

Given an array of N integers, find the average of all elements.

Example:

Input: arr = [10, 20, 30, 40, 50]
Output: 30.0

Code

Java

import java.util.Scanner;
public class ArrayAverage {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double sum = 0;
        for (int i = 0; i < n; i++) sum += sc.nextInt();
        System.out.println(sum / n);
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
print(sum(arr) / n)

Time: O(N)Space: O(1)

Question 10

Find the Median of the Given Array

Problem

Given an array, find the median. If N is odd, the middle element; if even, average of two middle.

Example:

Input: arr = [5, 3, 1, 4, 2]
Output: 3

Code

Java

import java.util.*;
public class ArrayMedian {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        Arrays.sort(arr);
        if (n % 2 == 1) System.out.println(arr[n / 2]);
        else System.out.println((arr[n / 2 - 1] + arr[n / 2]) / 2.0);
    }
}

Python

n = int(input())
arr = sorted(list(map(int, input().split())))
if n % 2 == 1:
    print(arr[n // 2])
else:
    print((arr[n // 2 - 1] + arr[n // 2]) / 2)

Time: O(N log N)Space: O(1)

Question 11

Remove Duplicates from a Sorted Array

Problem

Given a sorted array, remove duplicates in-place and return the new length.

Example:

Input: arr = [1, 1, 2, 2, 3, 4, 4]
Output: [1, 2, 3, 4], Length = 4

Code

Java

import java.util.Scanner;
public class RemoveDupsSorted {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int j = 0;
        for (int i = 1; i < n; i++) {
            if (arr[i] != arr[j]) arr[++j] = arr[i];
        }
        for (int i = 0; i <= j; i++) System.out.print(arr[i] + " ");
        System.out.println("\nLength = " + (j + 1));
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
result = list(dict.fromkeys(arr))
print(*result)
print("Length =", len(result))

Time: O(N)Space: O(1)

Question 12

Remove Duplicates from an Unsorted Array

Problem

Given an unsorted array, remove duplicates preserving first occurrence.

Example:

Input: arr = [4, 2, 3, 2, 1, 4]
Output: [4, 2, 3, 1]

Code

Java

import java.util.*;
public class RemoveDupsUnsorted {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        Set<Integer> seen = new LinkedHashSet<>();
        for (int x : arr) seen.add(x);
        for (int x : seen) System.out.print(x + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
print(*list(dict.fromkeys(arr)))

Time: O(N)Space: O(N)

Question 13

Adding Element in an Array

Problem

Given an array, a position P, and a value V, insert V at position P.

Example:

Input: arr = [1, 2, 4, 5], P = 2, V = 3
Output: [1, 2, 3, 4, 5]

Code

Java

import java.util.Scanner;
public class InsertElement {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n + 1];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int pos = sc.nextInt(), val = sc.nextInt();
        for (int i = n; i > pos; i--) arr[i] = arr[i - 1];
        arr[pos] = val;
        for (int i = 0; i <= n; i++) System.out.print(arr[i] + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
pos, val = map(int, input().split())
arr.insert(pos, val)
print(*arr)

Time: O(N)Space: O(1)

Question 14

Find All Repeating Elements in an Array

Problem

Given an array, find all elements that appear more than once.

Example:

Input: arr = [4, 2, 4, 5, 2, 3, 1]
Output: 4 2

Code

Java

import java.util.*;
public class RepeatingElements {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        Map<Integer, Integer> freq = new LinkedHashMap<>();
        for (int x : arr) freq.put(x, freq.getOrDefault(x, 0) + 1);
        for (Map.Entry<Integer, Integer> e : freq.entrySet())
            if (e.getValue() > 1) System.out.print(e.getKey() + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
from collections import Counter
print(*[k for k, v in Counter(arr).items() if v > 1])

Time: O(N)Space: O(N)

Question 15

Find All Non-Repeating Elements in an Array

Problem

Given an array, find all elements that appear exactly once.

Example:

Input: arr = [4, 2, 4, 5, 2, 3, 1]
Output: 5 3 1

Code

Java

import java.util.*;
public class NonRepeatingElements {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        Map<Integer, Integer> freq = new LinkedHashMap<>();
        for (int x : arr) freq.put(x, freq.getOrDefault(x, 0) + 1);
        for (Map.Entry<Integer, Integer> e : freq.entrySet())
            if (e.getValue() == 1) System.out.print(e.getKey() + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
from collections import Counter
print(*[k for k, v in Counter(arr).items() if v == 1])

Time: O(N)Space: O(N)

Question 16

Find All Symmetric Pairs in Array

Problem

Given an array of pairs (a, b), find all symmetric pairs where (b, a) also exists.

Example:

Input: pairs = [(1,2), (3,4), (2,1), (4,3)]
Output: (1,2)-(2,1), (3,4)-(4,3)

Code

Java

import java.util.*;
public class SymmetricPairs {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[][] pairs = new int[n][2];
        for (int i = 0; i < n; i++) { pairs[i][0] = sc.nextInt(); pairs[i][1] = sc.nextInt(); }
        Map<Integer, Integer> map = new HashMap<>();
        for (int[] p : pairs) {
            if (map.containsKey(p[1]) && map.get(p[1]) == p[0])
                System.out.println("(" + p[1] + "," + p[0] + ") - (" + p[0] + "," + p[1] + ")");
            else map.put(p[0], p[1]);
        }
    }
}

Python

n = int(input())
pairs = [tuple(map(int, input().split())) for _ in range(n)]
seen = {}
for a, b in pairs:
    if b in seen and seen[b] == a:
        print(f"({b},{a}) - ({a},{b})")
    else:
        seen[a] = b

Time: O(N)Space: O(N)

Question 17

Maximum Product Subarray in an Array

Problem

Given an array, find the contiguous subarray with the maximum product.

Example:

Input: arr = [2, 3, -2, 4]
Output: 6 (subarray [2, 3])

Code

Java

import java.util.Scanner;
public class MaxProductSubarray {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int maxProd = arr[0], currMax = arr[0], currMin = arr[0];
        for (int i = 1; i < n; i++) {
            if (arr[i] < 0) { int temp = currMax; currMax = currMin; currMin = temp; }
            currMax = Math.max(arr[i], currMax * arr[i]);
            currMin = Math.min(arr[i], currMin * arr[i]);
            maxProd = Math.max(maxProd, currMax);
        }
        System.out.println(maxProd);
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
max_prod = curr_max = curr_min = arr[0]
for i in range(1, n):
    if arr[i] < 0:
        curr_max, curr_min = curr_min, curr_max
    curr_max = max(arr[i], curr_max * arr[i])
    curr_min = min(arr[i], curr_min * arr[i])
    max_prod = max(max_prod, curr_max)
print(max_prod)

Time: O(N)Space: O(1)

Question 18

Replace Each Element of the Array by its Rank

Problem

Replace each element with its rank. Smallest gets rank 1, next gets 2, etc.

Example:

Input: arr = [20, 15, 26, 2, 98, 6]
Output: [4, 3, 5, 1, 6, 2]

Code

Java

import java.util.*;
public class RankReplacement {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int[] sorted = arr.clone();
        Arrays.sort(sorted);
        Map<Integer, Integer> rankMap = new HashMap<>();
        int rank = 1;
        for (int x : sorted) { if (!rankMap.containsKey(x)) rankMap.put(x, rank++); }
        for (int i = 0; i < n; i++) System.out.print(rankMap.get(arr[i]) + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
sorted_unique = sorted(set(arr))
rank_map = {v: i + 1 for i, v in enumerate(sorted_unique)}
print(*[rank_map[x] for x in arr])

Time: O(N log N)Space: O(N)

Question 19

Sorting Elements of an Array by Frequency

Problem

Sort elements by frequency (descending). If same frequency, sort by value (ascending).

Example:

Input: arr = [1, 2, 2, 3, 3, 3]
Output: [3, 3, 3, 2, 2, 1]

Code

Java

import java.util.*;
public class SortByFrequency {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        Map<Integer, Integer> freq = new HashMap<>();
        for (int x : arr) freq.put(x, freq.getOrDefault(x, 0) + 1);
        Integer[] boxed = Arrays.stream(arr).boxed().toArray(Integer[]::new);
        Arrays.sort(boxed, (a, b) -> freq.get(b) != freq.get(a) ? freq.get(b) - freq.get(a) : a - b);
        for (int x : boxed) System.out.print(x + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
from collections import Counter
freq = Counter(arr)
arr.sort(key=lambda x: (-freq[x], x))
print(*arr)

Time: O(N log N)Space: O(N)

Question 20

Rotation of Elements of Array - Left and Right

Problem

Given an array and K, perform both left and right rotation by K positions.

Example:

Input: arr = [1, 2, 3, 4, 5], K = 2
Left Rotation: [3, 4, 5, 1, 2]
Right Rotation: [4, 5, 1, 2, 3]

Code

Java

import java.util.Scanner;
public class LeftRightRotation {
    static void reverse(int[] arr, int s, int e) {
        while (s < e) { int t = arr[s]; arr[s] = arr[e]; arr[e] = t; s++; e--; }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(), k = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int[] left = arr.clone();
        int lk = k % n;
        reverse(left, 0, lk - 1); reverse(left, lk, n - 1); reverse(left, 0, n - 1);
        System.out.print("Left: ");
        for (int x : left) System.out.print(x + " ");
        int[] right = arr.clone();
        int rk = k % n;
        reverse(right, 0, n - rk - 1); reverse(right, n - rk, n - 1); reverse(right, 0, n - 1);
        System.out.print("\nRight: ");
        for (int x : right) System.out.print(x + " ");
    }
}

Python

n, k = map(int, input().split())
arr = list(map(int, input().split()))
k = k % n
print("Left:", *arr[k:] + arr[:k])
print("Right:", *arr[-k:] + arr[:-k])

Time: O(N)Space: O(N)

Question 21

Finding Equilibrium Index of an Array

Problem

Find the index where sum of left elements equals sum of right elements.

Example:

Input: arr = [-7, 1, 5, 2, -4, 3, 0]
Output: 3

Code

Java

import java.util.Scanner;
public class EquilibriumIndex {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        long totalSum = 0;
        for (int i = 0; i < n; i++) { arr[i] = sc.nextInt(); totalSum += arr[i]; }
        long leftSum = 0;
        for (int i = 0; i < n; i++) {
            totalSum -= arr[i];
            if (leftSum == totalSum) { System.out.println(i); return; }
            leftSum += arr[i];
        }
        System.out.println(-1);
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
total = sum(arr)
left = 0
for i in range(n):
    total -= arr[i]
    if left == total:
        print(i); break
    left += arr[i]
else:
    print(-1)

Time: O(N)Space: O(1)

Question 22

Finding Circular Rotation of an Array by K Positions

Problem

Perform circular right rotation of an array by K positions.

Example:

Input: arr = [1, 2, 3, 4, 5], K = 2
Output: [4, 5, 1, 2, 3]

Code

Java

import java.util.Scanner;
public class CircularRotation {
    static void reverse(int[] a, int s, int e) {
        while (s < e) { int t = a[s]; a[s] = a[e]; a[e] = t; s++; e--; }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(), k = sc.nextInt() % n;
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        reverse(arr, 0, n - 1);
        reverse(arr, 0, k - 1);
        reverse(arr, k, n - 1);
        for (int x : arr) System.out.print(x + " ");
    }
}

Python

n, k = map(int, input().split())
arr = list(map(int, input().split()))
k = k % n
print(*arr[-k:] + arr[:-k])

Time: O(N)Space: O(1)

Question 23

Sort an Array According to the Order Defined by Another Array

Problem

Sort array A so elements in B come first (in B's order), remaining elements sorted at end.

Example:

Input: A = [2, 1, 2, 5, 7, 1, 9, 3, 6, 8, 8], B = [2, 1, 8, 3]
Output: [2, 2, 1, 1, 8, 8, 3, 5, 6, 7, 9]

Code

Java

import java.util.*;
public class SortByOrder {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = sc.nextInt();
        int m = sc.nextInt();
        int[] b = new int[m];
        for (int i = 0; i < m; i++) b[i] = sc.nextInt();
        Map<Integer, Integer> freq = new TreeMap<>();
        for (int x : a) freq.put(x, freq.getOrDefault(x, 0) + 1);
        List<Integer> result = new ArrayList<>();
        for (int x : b) {
            if (freq.containsKey(x)) {
                for (int i = 0; i < freq.get(x); i++) result.add(x);
                freq.remove(x);
            }
        }
        for (Map.Entry<Integer, Integer> e : freq.entrySet())
            for (int i = 0; i < e.getValue(); i++) result.add(e.getKey());
        for (int x : result) System.out.print(x + " ");
    }
}

Python

n = int(input())
a = list(map(int, input().split()))
m = int(input())
b = list(map(int, input().split()))
from collections import Counter
freq = Counter(a)
result = []
for x in b:
    result.extend([x] * freq.pop(x, 0))
for x in sorted(freq.elements()):
    result.append(x)
print(*result)

Time: O(N log N)Space: O(N)

Question 24

Search an Element in an Array

Problem

Given an array and a target, find the index of the target. Return -1 if not found.

Example:

Input: arr = [10, 20, 30, 40, 50], target = 30
Output: 2

Code

Java

import java.util.Scanner;
public class SearchElement {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        int target = sc.nextInt(), idx = -1;
        for (int i = 0; i < n; i++) {
            if (arr[i] == target) { idx = i; break; }
        }
        System.out.println(idx);
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
target = int(input())
print(arr.index(target) if target in arr else -1)

Time: O(N)Space: O(1)

Question 25

Check if Array is a Subset of Another Array

Problem

Given two arrays A and B, check whether B is a subset of A.

Example:

Input: A = [11, 1, 13, 21, 3, 7], B = [11, 3, 7, 1]
Output: Yes

Code

Java

import java.util.*;
public class SubsetCheck {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = sc.nextInt();
        int m = sc.nextInt();
        int[] b = new int[m];
        for (int i = 0; i < m; i++) b[i] = sc.nextInt();
        Set<Integer> setA = new HashSet<>();
        for (int x : a) setA.add(x);
        boolean isSubset = true;
        for (int x : b) if (!setA.contains(x)) { isSubset = false; break; }
        System.out.println(isSubset ? "Yes" : "No");
    }
}

Python

n = int(input())
a = list(map(int, input().split()))
m = int(input())
b = list(map(int, input().split()))
print("Yes" if set(b).issubset(set(a)) else "No")

Time: O(N + M)Space: O(N)

Question 26

Check if a Number is Palindrome

Problem

Check whether a number reads the same forwards and backwards.

Example:

Input: 121
Output: Palindrome

Code

Java

import java.util.Scanner;
public class PalindromeNumber {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        int original = n, rev = 0;
        while (n > 0) { rev = rev * 10 + n % 10; n /= 10; }
        System.out.println(original == rev ? "Palindrome" : "Not Palindrome");
    }
}

#include <stdio.h>
int main() {
    int n, original, rev = 0;
    scanf("%d", &n);
    original = n;
    while (n > 0) { rev = rev * 10 + n % 10; n /= 10; }
    printf("%s\n", original == rev ? "Palindrome" : "Not Palindrome");
    return 0;
}

Python

n = input()
print("Palindrome" if n == n[::-1] else "Not Palindrome")

Time: O(D)Space: O(1)

Question 27

Find All Palindrome Numbers in a Given Range

Problem

Find all palindrome numbers in the range [L, R].

Example:

Input: L = 10, R = 130
Output: 11 22 33 44 55 66 77 88 99 101 111 121

Code

Java

import java.util.Scanner;
public class PalindromeRange {
    static boolean isPalin(int n) {
        int orig = n, rev = 0;
        while (n > 0) { rev = rev * 10 + n % 10; n /= 10; }
        return orig == rev;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int l = sc.nextInt(), r = sc.nextInt();
        for (int i = l; i <= r; i++) if (isPalin(i)) System.out.print(i + " ");
    }
}

Python

l, r = map(int, input().split())
for i in range(l, r + 1):
    s = str(i)
    if s == s[::-1]:
        print(i, end=" ")

Time: O((R-L) * D)Space: O(1)

Question 28

Check if a Number is Prime

Problem

Determine if a given integer N is a prime number.

Example:

Input: 17
Output: Prime

Code

Java

import java.util.Scanner;
public class PrimeCheck {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        if (n <= 1) { System.out.println("Not Prime"); return; }
        for (int i = 2; i * i <= n; i++)
            if (n % i == 0) { System.out.println("Not Prime"); return; }
        System.out.println("Prime");
    }
}

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    if (n <= 1) { printf("Not Prime\n"); return 0; }
    for (int i = 2; i * i <= n; i++)
        if (n % i == 0) { printf("Not Prime\n"); return 0; }
    printf("Prime\n");
    return 0;
}

Python

n = int(input())
if n <= 1:
    print("Not Prime")
else:
    print("Prime" if all(n % i != 0 for i in range(2, int(n**0.5) + 1)) else "Not Prime")

Time: O(sqrt(N))Space: O(1)

Question 29

Prime Numbers in a Given Range

Problem

Find all prime numbers in the range [L, R].

Example:

Input: L = 10, R = 30
Output: 11 13 17 19 23 29

Code

Java

import java.util.Scanner;
public class PrimeRange {
    static boolean isPrime(int n) {
        if (n <= 1) return false;
        for (int i = 2; i * i <= n; i++) if (n % i == 0) return false;
        return true;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int l = sc.nextInt(), r = sc.nextInt();
        for (int i = l; i <= r; i++) if (isPrime(i)) System.out.print(i + " ");
    }
}

Python

l, r = map(int, input().split())
for n in range(l, r + 1):
    if n > 1 and all(n % i != 0 for i in range(2, int(n**0.5) + 1)):
        print(n, end=" ")

Time: O((R-L) * sqrt(R))Space: O(1)

Question 30

Check if a Number is Armstrong Number

Problem

An Armstrong number of N digits: sum of each digit raised to Nth power equals the number.

Example:

Input: 153
Output: Armstrong (1^3 + 5^3 + 3^3 = 153)

Code

Java

import java.util.Scanner;
public class ArmstrongCheck {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        int original = n, sum = 0, digits = String.valueOf(n).length();
        int temp = n;
        while (temp > 0) { sum += Math.pow(temp % 10, digits); temp /= 10; }
        System.out.println(sum == original ? "Armstrong" : "Not Armstrong");
    }
}

Python

n = input()
digits = len(n)
total = sum(int(d) ** digits for d in n)
print("Armstrong" if total == int(n) else "Not Armstrong")

Time: O(D)Space: O(1)

Question 31

Check if a Number is Perfect Number

Problem

A perfect number equals the sum of its proper divisors. Check if N is perfect.

Example:

Input: 28
Output: Perfect Number (1 + 2 + 4 + 7 + 14 = 28)

Code

Java

import java.util.Scanner;
public class PerfectNumber {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        int sum = 0;
        for (int i = 1; i <= n / 2; i++) if (n % i == 0) sum += i;
        System.out.println(sum == n ? "Perfect Number" : "Not Perfect Number");
    }
}

Python

n = int(input())
s = sum(i for i in range(1, n) if n % i == 0)
print("Perfect Number" if s == n else "Not Perfect Number")

Time: O(N)Space: O(1)

Question 32

Even or Odd

Problem

Determine if a given integer is even or odd.

Example:

Input: 7
Output: Odd

Code

Java

import java.util.Scanner;
public class EvenOdd {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        System.out.println(n % 2 == 0 ? "Even" : "Odd");
    }
}

Python

n = int(input())
print("Even" if n % 2 == 0 else "Odd")

Time: O(1)Space: O(1)

Question 33

Check Whether a Number is Positive or Negative

Problem

Determine if a number is positive, negative, or zero.

Example:

Input: -5
Output: Negative

Code

Java

import java.util.Scanner;
public class PositiveNegative {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        System.out.println(n > 0 ? "Positive" : n < 0 ? "Negative" : "Zero");
    }
}

Python

n = int(input())
print("Positive" if n > 0 else "Negative" if n < 0 else "Zero")

Time: O(1)Space: O(1)

Question 34

Sum of First N Natural Numbers

Problem

Find the sum of first N natural numbers.

Example:

Input: 10
Output: 55

Code

Java

import java.util.Scanner;
public class SumNatural {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        System.out.println(n * (n + 1) / 2);
    }
}

Python

n = int(input())
print(n * (n + 1) // 2)

Time: O(1)Space: O(1)

Question 35

Find Sum of AP Series

Problem

Given first term A, common difference D, and N terms, find the sum.

Example:

Input: A = 1, D = 2, N = 5
Output: 25

Code

Java

import java.util.Scanner;
public class APSum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble(), d = sc.nextDouble();
        int n = sc.nextInt();
        System.out.println((n / 2.0) * (2 * a + (n - 1) * d));
    }
}

Python

a, d, n = map(float, input().split())
n = int(n)
print(n / 2 * (2 * a + (n - 1) * d))

Time: O(1)Space: O(1)

Question 36

Program to Find Sum of GP Series

Problem

Given first term A, common ratio R, and N terms, find the sum.

Example:

Input: A = 2, R = 3, N = 4
Output: 80

Code

Java

import java.util.Scanner;
public class GPSum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble(), r = sc.nextDouble();
        int n = sc.nextInt();
        System.out.println(r == 1 ? a * n : a * (Math.pow(r, n) - 1) / (r - 1));
    }
}

Python

a, r, n = map(float, input().split())
n = int(n)
print(a * n if r == 1 else a * (r**n - 1) / (r - 1))

Time: O(1)Space: O(1)

Question 37

Greatest of Two Numbers

Problem

Find the greater of two integers.

Code

Java

import java.util.Scanner;
public class GreatestOfTwo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt();
        System.out.println(Math.max(a, b));
    }
}

Python

a, b = map(int, input().split())
print(max(a, b))

Time: O(1)Space: O(1)

Question 38

Greatest of Three Numbers

Problem

Find the greatest of three integers.

Code

Java

import java.util.Scanner;
public class GreatestOfThree {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt();
        System.out.println(Math.max(a, Math.max(b, c)));
    }
}

Python

a, b, c = map(int, input().split())
print(max(a, b, c))

Time: O(1)Space: O(1)

Question 39

Leap Year or Not

Problem

Check whether a given year is a leap year.

Example:

Input: 2024
Output: Leap Year

Code

Java

import java.util.Scanner;
public class LeapYear {
    public static void main(String[] args) {
        int y = new Scanner(System.in).nextInt();
        System.out.println((y % 4 == 0 && y % 100 != 0) || y % 400 == 0 ? "Leap Year" : "Not Leap Year");
    }
}

Python

y = int(input())
print("Leap Year" if (y % 4 == 0 and y % 100 != 0) or y % 400 == 0 else "Not Leap Year")

Time: O(1)Space: O(1)

Question 40

Reverse Digits of a Number

Problem

Reverse the digits of an integer.

Example:

Input: 12345
Output: 54321

Code

Java

import java.util.Scanner;
public class ReverseDigits {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt(), rev = 0;
        while (n != 0) { rev = rev * 10 + n % 10; n /= 10; }
        System.out.println(rev);
    }
}

Python

n = input()
print(n[::-1])

Time: O(D)Space: O(1)

Question 41

Maximum and Minimum Digit in a Number

Problem

Find the largest and smallest digit in a number.

Example:

Input: 4518
Output: Max = 8, Min = 1

Code

Java

import java.util.Scanner;
public class MaxMinDigit {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        int max = 0, min = 9;
        while (n > 0) {
            int d = n % 10;
            if (d > max) max = d;
            if (d < min) min = d;
            n /= 10;
        }
        System.out.println("Max = " + max + ", Min = " + min);
    }
}

Python

n = input()
digits = [int(d) for d in n]
print(f"Max = {max(digits)}, Min = {min(digits)}")

Time: O(D)Space: O(1)

Question 42

Print Fibonacci up to Nth Term

Problem

Print the Fibonacci sequence up to the Nth term.

Example:

Input: 8
Output: 0 1 1 2 3 5 8 13

Code

Java

import java.util.Scanner;
public class Fibonacci {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        int a = 0, b = 1;
        for (int i = 0; i < n; i++) {
            System.out.print(a + " ");
            int c = a + b; a = b; b = c;
        }
    }
}

Python

n = int(input())
a, b = 0, 1
for _ in range(n):
    print(a, end=" ")
    a, b = b, a + b

Time: O(N)Space: O(1)

Question 43

Factorial of a Number

Problem

Compute N! (N factorial).

Example:

Input: 5
Output: 120

Code

Java

import java.util.Scanner;
public class Factorial {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        long fact = 1;
        for (int i = 2; i <= n; i++) fact *= i;
        System.out.println(fact);
    }
}

Python

import math
n = int(input())
print(math.factorial(n))

Time: O(N)Space: O(1)

Question 44

Power of a Number

Problem

Compute B raised to the power E.

Example:

Input: B = 2, E = 10
Output: 1024

Code

Java

import java.util.Scanner;
public class Power {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long b = sc.nextLong(), e = sc.nextLong(), result = 1;
        while (e > 0) {
            if (e % 2 == 1) result *= b;
            b *= b; e /= 2;
        }
        System.out.println(result);
    }
}

Python

b, e = map(int, input().split())
print(b ** e)

Time: O(log E)Space: O(1)

Question 45

Factors of a Given Number

Problem

Print all factors (divisors) of N.

Example:

Input: 12
Output: 1 2 3 4 6 12

Code

Java

import java.util.Scanner;
public class Factors {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        for (int i = 1; i <= n; i++) if (n % i == 0) System.out.print(i + " ");
    }
}

Python

n = int(input())
print(*[i for i in range(1, n + 1) if n % i == 0])

Time: O(N)Space: O(1)

Question 46

Print All Prime Factors of a Number

Problem

Print all prime factors of N.

Example:

Input: 60
Output: 2 3 5

Code

Java

import java.util.Scanner;
public class PrimeFactors {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        for (int i = 2; i * i <= n; i++) {
            if (n % i == 0) {
                System.out.print(i + " ");
                while (n % i == 0) n /= i;
            }
        }
        if (n > 1) System.out.print(n);
    }
}

Python

n = int(input())
i = 2
factors = []
while i * i <= n:
    if n % i == 0:
        factors.append(i)
        while n % i == 0: n //= i
    i += 1
if n > 1: factors.append(n)
print(*factors)

Time: O(sqrt(N))Space: O(1)

Question 47

Check if a Number is a Strong Number

Problem

A strong number: sum of factorial of each digit equals the number.

Example:

Input: 145
Output: Strong Number (1! + 4! + 5! = 145)

Code

Java

import java.util.Scanner;
public class StrongNumber {
    static int factorial(int n) { int f = 1; for (int i = 2; i <= n; i++) f *= i; return f; }
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt(), original = n, sum = 0;
        while (n > 0) { sum += factorial(n % 10); n /= 10; }
        System.out.println(sum == original ? "Strong Number" : "Not Strong Number");
    }
}

Python

import math
n = int(input())
print("Strong Number" if sum(math.factorial(int(d)) for d in str(n)) == n else "Not Strong Number")

Time: O(D)Space: O(1)

Question 48

Check if a Number is Automorphic

Problem

An automorphic number's square ends with the number itself.

Example:

Input: 25
Output: Automorphic (25^2 = 625)

Code

Java

import java.util.Scanner;
public class Automorphic {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        long sq = (long) n * n;
        System.out.println(String.valueOf(sq).endsWith(String.valueOf(n)) ? "Automorphic" : "Not Automorphic");
    }
}

Python

n = int(input())
print("Automorphic" if str(n * n).endswith(str(n)) else "Not Automorphic")

Time: O(1)Space: O(1)

Question 49

GCD of Two Numbers

Problem

Find the Greatest Common Divisor of two numbers.

Example:

Input: 12 18
Output: 6

Code

Java

import java.util.Scanner;
public class GCD {
    static int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println(gcd(sc.nextInt(), sc.nextInt()));
    }
}

Python

import math
a, b = map(int, input().split())
print(math.gcd(a, b))

Time: O(log(min(A,B)))Space: O(1)

Question 50

LCM of Two Numbers

Problem

Find the Least Common Multiple of two numbers.

Example:

Input: 4 6
Output: 12

Code

Java

import java.util.Scanner;
public class LCM {
    static int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt();
        System.out.println(a / gcd(a, b) * b);
    }
}

Python

import math
a, b = map(int, input().split())
print(a * b // math.gcd(a, b))

Time: O(log(min(A,B)))Space: O(1)

Question 51

Check if a Number is Harshad Number

Problem

A Harshad number is divisible by the sum of its digits.

Example:

Input: 18
Output: Harshad Number (18 divisible by 1+8=9)

Code

Java

import java.util.Scanner;
public class HarshadNumber {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt(), sum = 0, temp = n;
        while (temp > 0) { sum += temp % 10; temp /= 10; }
        System.out.println(n % sum == 0 ? "Harshad Number" : "Not Harshad Number");
    }
}

Python

n = int(input())
s = sum(int(d) for d in str(n))
print("Harshad Number" if n % s == 0 else "Not Harshad Number")

Time: O(D)Space: O(1)

Question 52

Check if a Number is Abundant

Problem

An abundant number has sum of proper divisors greater than itself.

Example:

Input: 12
Output: Abundant Number (1+2+3+4+6 = 16 > 12)

Code

Java

import java.util.Scanner;
public class AbundantNumber {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt(), sum = 0;
        for (int i = 1; i <= n / 2; i++) if (n % i == 0) sum += i;
        System.out.println(sum > n ? "Abundant Number" : "Not Abundant Number");
    }
}

Python

n = int(input())
s = sum(i for i in range(1, n) if n % i == 0)
print("Abundant Number" if s > n else "Not Abundant Number")

Time: O(N)Space: O(1)

Question 53

Sum of Digits of a Number

Problem

Find the sum of digits of N.

Example:

Input: 1234
Output: 10

Code

Java

import java.util.Scanner;
public class DigitSum {
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt(), sum = 0;
        while (n > 0) { sum += n % 10; n /= 10; }
        System.out.println(sum);
    }
}

Python

n = input()
print(sum(int(d) for d in n))

Time: O(D)Space: O(1)

Question 54

Sum of Numbers in a Given Range

Problem

Find the sum of all numbers from L to R.

Example:

Input: L = 3, R = 7
Output: 25

Code

Java

import java.util.Scanner;
public class RangeSum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long l = sc.nextLong(), r = sc.nextLong();
        System.out.println(r * (r + 1) / 2 - (l - 1) * l / 2);
    }
}

Python

l, r = map(int, input().split())
print(r * (r + 1) // 2 - (l - 1) * l // 2)

Time: O(1)Space: O(1)

Question 55

Permutations nPr

Problem

Compute nPr = N! / (N-R)!

Example:

Input: N = 5, R = 3
Output: 60

Code

Java

import java.util.Scanner;
public class Permutations {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(), r = sc.nextInt();
        long result = 1;
        for (int i = n; i > n - r; i--) result *= i;
        System.out.println(result);
    }
}

Python

import math
n, r = map(int, input().split())
print(math.perm(n, r))

Time: O(R)Space: O(1)

Question 56

Program to Add Two Fractions

Problem

Add two fractions a/b and c/d, output in simplest form.

Example:

Input: 1/3 + 1/6
Output: 1/2

Code

Java

import java.util.Scanner;
public class AddFractions {
    static int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
        int num = a * d + c * b, den = b * d;
        int g = gcd(Math.abs(num), Math.abs(den));
        System.out.println(num / g + "/" + den / g);
    }
}

Python

from math import gcd
a, b, c, d = map(int, input().split())
num = a * d + c * b
den = b * d
g = gcd(abs(num), abs(den))
print(f"{num // g}/{den // g}")

Time: O(log(min(num,den)))Space: O(1)

Question 57

Replace All 0s with 1s in a Given Integer

Problem

Replace every digit 0 with 1 in the number.

Example:

Input: 102030
Output: 112131

Code

Java

import java.util.Scanner;
public class ReplaceZeros {
    public static void main(String[] args) {
        System.out.println(new Scanner(System.in).next().replace('0', '1'));
    }
}

Python

print(input().replace('0', '1'))

Time: O(D)Space: O(D)

Question 58

Can a Number be Expressed as Sum of Two Primes

Problem

Check if N can be expressed as the sum of two prime numbers.

Example:

Input: 10
Output: Yes (3 + 7)

Code

Java

import java.util.Scanner;
public class SumTwoPrimes {
    static boolean isPrime(int n) {
        if (n <= 1) return false;
        for (int i = 2; i * i <= n; i++) if (n % i == 0) return false;
        return true;
    }
    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();
        for (int i = 2; i <= n / 2; i++) {
            if (isPrime(i) && isPrime(n - i)) {
                System.out.println("Yes (" + i + " + " + (n - i) + ")"); return;
            }
        }
        System.out.println("No");
    }
}

Python

def is_prime(n):
    if n <= 1: return False
    return all(n % i != 0 for i in range(2, int(n**0.5) + 1))

n = int(input())
for i in range(2, n // 2 + 1):
    if is_prime(i) and is_prime(n - i):
        print(f"Yes ({i} + {n - i})"); break
else:
    print("No")

Time: O(N * sqrt(N))Space: O(1)

Question 59

Calculate the Area of a Circle

Problem

Given radius R, calculate the area.

Example:

Input: R = 5
Output: 78.54

Code

Java

import java.util.Scanner;
public class CircleArea {
    public static void main(String[] args) {
        double r = new Scanner(System.in).nextDouble();
        System.out.printf("%.2f%n", Math.PI * r * r);
    }
}

Python

import math
r = float(input())
print(f"{math.pi * r * r:.2f}")

Time: O(1)Space: O(1)

Question 60

Find Roots of a Quadratic Equation

Problem

Given coefficients A, B, C of Ax^2 + Bx + C = 0, find the roots.

Example:

Input: A = 1, B = -3, C = 2
Output: Roots are 2.0 and 1.0

Code

Java

import java.util.Scanner;
public class QuadraticRoots {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble(), b = sc.nextDouble(), c = sc.nextDouble();
        double disc = b * b - 4 * a * c;
        if (disc > 0) {
            System.out.println("Roots: " + (-b + Math.sqrt(disc)) / (2*a) + " and " + (-b - Math.sqrt(disc)) / (2*a));
        } else if (disc == 0) {
            System.out.println("Root: " + (-b / (2 * a)));
        } else {
            double real = -b / (2*a), imag = Math.sqrt(-disc) / (2*a);
            System.out.println("Roots: " + real + "+" + imag + "i and " + real + "-" + imag + "i");
        }
    }
}

Python

import cmath
a, b, c = map(float, input().split())
disc = b**2 - 4*a*c
r1 = (-b + cmath.sqrt(disc)) / (2*a)
r2 = (-b - cmath.sqrt(disc)) / (2*a)
print(f"Roots are {r1} and {r2}")

Time: O(1)Space: O(1)

Question 61

Convert Binary to Decimal

Problem

Convert a binary number to decimal.

Example:

Input: 1010
Output: 10

Code

Java

import java.util.Scanner;
public class BinaryToDecimal {
    public static void main(String[] args) {
        System.out.println(Integer.parseInt(new Scanner(System.in).next(), 2));
    }
}

Python

print(int(input(), 2))

Time: O(D)Space: O(1)

Question 62

Convert Binary to Octal

Problem

Convert a binary number to octal.

Example:

Input: 110101
Output: 65

Code

Java

import java.util.Scanner;
public class BinaryToOctal {
    public static void main(String[] args) {
        String binary = new Scanner(System.in).next();
        System.out.println(Integer.toOctalString(Integer.parseInt(binary, 2)));
    }
}

Python

print(oct(int(input(), 2))[2:])

Time: O(D)Space: O(D)

Question 63

Decimal to Binary Conversion

Problem

Convert a decimal number to binary.

Example:

Input: 10
Output: 1010

Code

Java

import java.util.Scanner;
public class DecimalToBinary {
    public static void main(String[] args) {
        System.out.println(Integer.toBinaryString(new Scanner(System.in).nextInt()));
    }
}

Python

print(bin(int(input()))[2:])

Time: O(log N)Space: O(log N)

Question 64

Convert Decimal to Octal

Problem

Convert a decimal number to octal.

Example:

Input: 100
Output: 144

Code

Java

import java.util.Scanner;
public class DecimalToOctal {
    public static void main(String[] args) {
        System.out.println(Integer.toOctalString(new Scanner(System.in).nextInt()));
    }
}

Python

print(oct(int(input()))[2:])

Time: O(log N)Space: O(log N)

Question 65

Convert Octal to Binary

Problem

Convert an octal number to binary.

Example:

Input: 17
Output: 1111

Code

Java

import java.util.Scanner;
public class OctalToBinary {
    public static void main(String[] args) {
        String octal = new Scanner(System.in).next();
        System.out.println(Integer.toBinaryString(Integer.parseInt(octal, 8)));
    }
}

Python

print(bin(int(input(), 8))[2:])

Time: O(D)Space: O(D)

Question 66

Convert Octal to Decimal

Problem

Convert an octal number to decimal.

Example:

Input: 17
Output: 15

Code

Java

import java.util.Scanner;
public class OctalToDecimal {
    public static void main(String[] args) {
        System.out.println(Integer.parseInt(new Scanner(System.in).next(), 8));
    }
}

Python

print(int(input(), 8))

Time: O(D)Space: O(1)

Question 67

Convert Digits or Numbers to Words

Problem

Convert each digit of a number to its English word.

Example:

Input: 123
Output: One Two Three

Code

Java

import java.util.Scanner;
public class DigitsToWords {
    public static void main(String[] args) {
        String n = new Scanner(System.in).next();
        String[] words = {"Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine"};
        for (char c : n.toCharArray()) System.out.print(words[c - '0'] + " ");
    }
}

Python

n = input()
words = ["Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine"]
print(" ".join(words[int(d)] for d in n))

Time: O(D)Space: O(1)

Question 68

Bubble Sort Algorithm

Problem

Implement Bubble Sort to sort an array in ascending order.

Example:

Input: arr = [64, 34, 25, 12, 22, 11, 90]
Output: [11, 12, 22, 25, 34, 64, 90]

Code

Java

import java.util.Scanner;
public class BubbleSort {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        for (int i = 0; i < n - 1; i++) {
            boolean swapped = false;
            for (int j = 0; j < n - 1 - i; j++) {
                if (arr[j] > arr[j + 1]) {
                    int temp = arr[j]; arr[j] = arr[j + 1]; arr[j + 1] = temp;
                    swapped = true;
                }
            }
            if (!swapped) break;
        }
        for (int x : arr) System.out.print(x + " ");
    }
}

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    int arr[n];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);
    for (int i = 0; i < n - 1; i++) {
        int swapped = 0;
        for (int j = 0; j < n - 1 - i; j++) {
            if (arr[j] > arr[j + 1]) {
                int t = arr[j]; arr[j] = arr[j + 1]; arr[j + 1] = t;
                swapped = 1;
            }
        }
        if (!swapped) break;
    }
    for (int i = 0; i < n; i++) printf("%d ", arr[i]);
    return 0;
}

Python

n = int(input())
arr = list(map(int, input().split()))
for i in range(n - 1):
    swapped = False
    for j in range(n - 1 - i):
        if arr[j] > arr[j + 1]:
            arr[j], arr[j + 1] = arr[j + 1], arr[j]
            swapped = True
    if not swapped: break
print(*arr)

Time: O(N^2)Space: O(1)

Question 69

Selection Sort Algorithm

Problem

Implement Selection Sort to sort an array in ascending order.

Example:

Input: arr = [64, 25, 12, 22, 11]
Output: [11, 12, 22, 25, 64]

Code

Java

import java.util.Scanner;
public class SelectionSort {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        for (int i = 0; i < n - 1; i++) {
            int minIdx = i;
            for (int j = i + 1; j < n; j++) if (arr[j] < arr[minIdx]) minIdx = j;
            int temp = arr[i]; arr[i] = arr[minIdx]; arr[minIdx] = temp;
        }
        for (int x : arr) System.out.print(x + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
for i in range(n - 1):
    min_idx = i
    for j in range(i + 1, n):
        if arr[j] < arr[min_idx]: min_idx = j
    arr[i], arr[min_idx] = arr[min_idx], arr[i]
print(*arr)

Time: O(N^2)Space: O(1)

Question 70

Insertion Sort Algorithm

Problem

Implement Insertion Sort to sort an array in ascending order.

Example:

Input: arr = [12, 11, 13, 5, 6]
Output: [5, 6, 11, 12, 13]

Code

Java

import java.util.Scanner;
public class InsertionSort {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        for (int i = 1; i < n; i++) {
            int key = arr[i], j = i - 1;
            while (j >= 0 && arr[j] > key) { arr[j + 1] = arr[j]; j--; }
            arr[j + 1] = key;
        }
        for (int x : arr) System.out.print(x + " ");
    }
}

Python

n = int(input())
arr = list(map(int, input().split()))
for i in range(1, n):
    key = arr[i]
    j = i - 1
    while j >= 0 and arr[j] > key:
        arr[j + 1] = arr[j]; j -= 1
    arr[j + 1] = key
print(*arr)

Time: O(N^2)Space: O(1)

Question 71

Quick Sort Algorithm

Problem

Implement Quick Sort to sort an array in ascending order.

Example:

Input: arr = [10, 7, 8, 9, 1, 5]
Output: [1, 5, 7, 8, 9, 10]

Code

Java

import java.util.Scanner;
public class QuickSort {
    static void quickSort(int[] arr, int low, int high) {
        if (low < high) {
            int pi = partition(arr, low, high);
            quickSort(arr, low, pi - 1);
            quickSort(arr, pi + 1, high);
        }
    }
    static int partition(int[] arr, int low, int high) {
        int pivot = arr[high], i = low - 1;
        for (int j = low; j < high; j++) {
            if (arr[j] < pivot) { i++; int t = arr[i]; arr[i] = arr[j]; arr[j] = t; }
        }
        int t = arr[i + 1]; arr[i + 1] = arr[high]; arr[high] = t;
        return i + 1;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        quickSort(arr, 0, n - 1);
        for (int x : arr) System.out.print(x + " ");
    }
}

Python

def quick_sort(arr):
    if len(arr) <= 1: return arr
    pivot = arr[-1]
    left = [x for x in arr[:-1] if x <= pivot]
    right = [x for x in arr[:-1] if x > pivot]
    return quick_sort(left) + [pivot] + quick_sort(right)

n = int(input())
arr = list(map(int, input().split()))
print(*quick_sort(arr))

Time: O(N log N) average, O(N^2) worstSpace: O(log N)

Question 72

Merge Sort Algorithm

Problem

Implement Merge Sort to sort an array in ascending order.

Example:

Input: arr = [38, 27, 43, 3, 9, 82, 10]
Output: [3, 9, 10, 27, 38, 43, 82]

Code

Java

import java.util.Scanner;
public class MergeSort {
    static void merge(int[] arr, int l, int m, int r) {
        int[] left = new int[m - l + 1], right = new int[r - m];
        System.arraycopy(arr, l, left, 0, left.length);
        System.arraycopy(arr, m + 1, right, 0, right.length);
        int i = 0, j = 0, k = l;
        while (i < left.length && j < right.length)
            arr[k++] = left[i] <= right[j] ? left[i++] : right[j++];
        while (i < left.length) arr[k++] = left[i++];
        while (j < right.length) arr[k++] = right[j++];
    }
    static void mergeSort(int[] arr, int l, int r) {
        if (l < r) {
            int m = (l + r) / 2;
            mergeSort(arr, l, m);
            mergeSort(arr, m + 1, r);
            merge(arr, l, m, r);
        }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) arr[i] = sc.nextInt();
        mergeSort(arr, 0, n - 1);
        for (int x : arr) System.out.print(x + " ");
    }
}

Python

def merge_sort(arr):
    if len(arr) <= 1: return arr
    mid = len(arr) // 2
    left = merge_sort(arr[:mid])
    right = merge_sort(arr[mid:])
    result, i, j = [], 0, 0
    while i < len(left) and j < len(right):
        if left[i] <= right[j]: result.append(left[i]); i += 1
        else: result.append(right[j]); j += 1
    return result + left[i:] + right[j:]

n = int(input())
arr = list(map(int, input().split()))
print(*merge_sort(arr))

Time: O(N log N)Space: O(N)

Question 73

Check if a String is Palindrome

Problem

Check whether a string reads the same forwards and backwards.

Example:

Input: "madam"
Output: Palindrome

Code

Java

import java.util.Scanner;
public class StringPalindrome {
    public static void main(String[] args) {
        String s = new Scanner(System.in).next();
        System.out.println(s.equals(new StringBuilder(s).reverse().toString()) ? "Palindrome" : "Not Palindrome");
    }
}

Python

s = input()
print("Palindrome" if s == s[::-1] else "Not Palindrome")

Time: O(N)Space: O(N)

Question 74

Count Vowels, Consonants, and Spaces in a String

Problem

Count the number of vowels, consonants, and spaces in a string.

Example:

Input: "Hello World"
Output: Vowels: 3, Consonants: 7, Spaces: 1

Code

Java

import java.util.Scanner;
public class CountVowelsConsonants {
    public static void main(String[] args) {
        String s = new Scanner(System.in).nextLine().toLowerCase();
        int v = 0, c = 0, sp = 0;
        for (char ch : s.toCharArray()) {
            if (ch == ' ') sp++;
            else if ("aeiou".indexOf(ch) >= 0) v++;
            else if (Character.isLetter(ch)) c++;
        }
        System.out.println("Vowels: " + v + ", Consonants: " + c + ", Spaces: " + sp);
    }
}

Python

s = input()
vowels = sum(1 for c in s if c.lower() in 'aeiou')
consonants = sum(1 for c in s if c.isalpha() and c.lower() not in 'aeiou')
spaces = s.count(' ')
print(f"Vowels: {vowels}, Consonants: {consonants}, Spaces: {spaces}")

Time: O(N)Space: O(1)

Question 75

Find the ASCII Value of a Character

Problem

Find the ASCII value of a given character.

Example:

Input: A
Output: 65

Code

Java

import java.util.Scanner;
public class ASCIIValue {
    public static void main(String[] args) {
        char c = new Scanner(System.in).next().charAt(0);
        System.out.println((int) c);
    }
}

Python

print(ord(input()))

Time: O(1)Space: O(1)

Question 76

Remove All Vowels from a String

Problem

Remove all vowels from the given string.

Example:

Input: "Hello World"
Output: "Hll Wrld"

Code

Java

import java.util.Scanner;
public class RemoveVowels {
    public static void main(String[] args) {
        System.out.println(new Scanner(System.in).nextLine().replaceAll("[aeiouAEIOU]", ""));
    }
}

Python

s = input()
print(''.join(c for c in s if c.lower() not in 'aeiou'))

Time: O(N)Space: O(N)

Question 77

Remove Spaces from a String

Problem

Remove all spaces from the given string.

Example:

Input: "Hello World Program"
Output: "HelloWorldProgram"

Code

Java

import java.util.Scanner;
public class RemoveSpaces {
    public static void main(String[] args) {
        System.out.println(new Scanner(System.in).nextLine().replace(" ", ""));
    }
}

Python

print(input().replace(" ", ""))

Time: O(N)Space: O(N)

Question 78

Remove Characters Except Alphabets

Problem

Remove all non-alphabetic characters from a string.

Example:

Input: "Hello123 World!@#"
Output: "HelloWorld"

Code

Java

import java.util.Scanner;
public class RemoveNonAlpha {
    public static void main(String[] args) {
        System.out.println(new Scanner(System.in).nextLine().replaceAll("[^a-zA-Z]", ""));
    }
}

Python

print(''.join(c for c in input() if c.isalpha()))

Time: O(N)Space: O(N)

Question 79

Reverse a String

Problem

Reverse the given string.

Example:

Input: "Hello"
Output: "olleH"

Code

Java

import java.util.Scanner;
public class ReverseString {
    public static void main(String[] args) {
        System.out.println(new StringBuilder(new Scanner(System.in).nextLine()).reverse());
    }
}

#include <stdio.h>
#include <string.h>
int main() {
    char s[1000];
    scanf("%s", s);
    int n = strlen(s);
    for (int i = 0; i < n / 2; i++) { char t = s[i]; s[i] = s[n-1-i]; s[n-1-i] = t; }
    printf("%s\n", s);
    return 0;
}

Python

print(input()[::-1])

Time: O(N)Space: O(N)

Question 80

Remove Brackets from an Algebraic Expression

Problem

Remove all brackets from an algebraic expression.

Example:

Input: "(a+b)*(c-d)"
Output: "a+b*c-d"

Code

Java

import java.util.Scanner;
public class RemoveBrackets {
    public static void main(String[] args) {
        System.out.println(new Scanner(System.in).nextLine().replaceAll("[(){}\\[\\]]", ""));
    }
}

Python

import re
print(re.sub(r'[(){}\[\]]', '', input()))

Time: O(N)Space: O(N)

Question 81

Sum of the Numbers in a String

Problem

Find the sum of all numbers embedded in a string.

Example:

Input: "abc12cd34ef5"
Output: 51 (12 + 34 + 5)

Code

Java

import java.util.Scanner;
public class SumNumbersInString {
    public static void main(String[] args) {
        String s = new Scanner(System.in).nextLine();
        int sum = 0, num = 0;
        boolean inNum = false;
        for (char c : s.toCharArray()) {
            if (Character.isDigit(c)) { num = num * 10 + (c - '0'); inNum = true; }
            else { if (inNum) { sum += num; num = 0; inNum = false; } }
        }
        if (inNum) sum += num;
        System.out.println(sum);
    }
}

Python

import re
print(sum(int(x) for x in re.findall(r'\d+', input())))

Time: O(N)Space: O(1)

Question 82

Capitalize First and Last Character of Each Word

Problem

Capitalize the first and last character of each word in a string.

Example:

Input: "hello world program"
Output: "HellO WorlD PrograM"

Code

Java

import java.util.Scanner;
public class CapitalizeFirstLast {
    public static void main(String[] args) {
        String[] words = new Scanner(System.in).nextLine().split(" ");
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < words.length; i++) {
            if (i > 0) sb.append(" ");
            String w = words[i];
            if (w.length() == 1) sb.append(w.toUpperCase());
            else sb.append(Character.toUpperCase(w.charAt(0))).append(w.substring(1, w.length()-1)).append(Character.toUpperCase(w.charAt(w.length()-1)));
        }
        System.out.println(sb);
    }
}

Python

s = input()
result = []
for word in s.split(' '):
    if len(word) <= 1: result.append(word.upper())
    else: result.append(word[0].upper() + word[1:-1] + word[-1].upper())
print(' '.join(result))

Time: O(N)Space: O(N)

Question 83

Calculate Frequency of Characters in a String

Problem

Count the frequency of each character in a string.

Example:

Input: "hello"
Output: h->1, e->1, l->2, o->1

Code

Java

import java.util.*;
public class CharFrequency {
    public static void main(String[] args) {
        String s = new Scanner(System.in).nextLine();
        Map<Character, Integer> freq = new LinkedHashMap<>();
        for (char c : s.toCharArray()) freq.put(c, freq.getOrDefault(c, 0) + 1);
        for (Map.Entry<Character, Integer> e : freq.entrySet())
            System.out.println(e.getKey() + " -> " + e.getValue());
    }
}

Python

from collections import Counter
for ch, cnt in Counter(input()).items():
    print(f"{ch} -> {cnt}")

Time: O(N)Space: O(1)

Question 84

Find Non-Repeating Characters of a String

Problem

Find all characters that appear exactly once.

Example:

Input: "hello"
Output: h e o

Code

Java

import java.util.*;
public class NonRepeatingChars {
    public static void main(String[] args) {
        String s = new Scanner(System.in).next();
        Map<Character, Integer> freq = new LinkedHashMap<>();
        for (char c : s.toCharArray()) freq.put(c, freq.getOrDefault(c, 0) + 1);
        for (Map.Entry<Character, Integer> e : freq.entrySet())
            if (e.getValue() == 1) System.out.print(e.getKey() + " ");
    }
}

Python

from collections import Counter
s = input()
freq = Counter(s)
print(*[c for c in s if freq[c] == 1])

Time: O(N)Space: O(1)

Question 85

Check if Two Strings are Anagram

Problem

Check if two strings contain the same characters with same frequency.

Example:

Input: "listen" "silent"
Output: Anagram

Code

Java

import java.util.*;
public class AnagramCheck {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray(), b = sc.next().toCharArray();
        Arrays.sort(a); Arrays.sort(b);
        System.out.println(Arrays.equals(a, b) ? "Anagram" : "Not Anagram");
    }
}

Python

a, b = input().split()
print("Anagram" if sorted(a) == sorted(b) else "Not Anagram")

Time: O(N log N)Space: O(1)

Question 86

Count Common Subsequence in Two Strings

Problem

Find the length of the longest common subsequence.

Example:

Input: "ABCBDAB" "BDCAB"
Output: 4 (BCAB)

Code

Java

import java.util.Scanner;
public class LCS {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String a = sc.next(), b = sc.next();
        int m = a.length(), n = b.length();
        int[][] dp = new int[m + 1][n + 1];
        for (int i = 1; i <= m; i++)
            for (int j = 1; j <= n; j++)
                dp[i][j] = a.charAt(i-1) == b.charAt(j-1) ? dp[i-1][j-1] + 1 : Math.max(dp[i-1][j], dp[i][j-1]);
        System.out.println(dp[m][n]);
    }
}

Python

a, b = input().split()
m, n = len(a), len(b)
dp = [[0] * (n + 1) for _ in range(m + 1)]
for i in range(1, m + 1):
    for j in range(1, n + 1):
        dp[i][j] = dp[i-1][j-1] + 1 if a[i-1] == b[j-1] else max(dp[i-1][j], dp[i][j-1])
print(dp[m][n])

Time: O(M * N)Space: O(M * N)

Question 87

Wildcard Pattern Matching

Problem

Match text against pattern with '?' (any single char) and '*' (zero or more chars).

Example:

Input: text = "baaabab", pattern = "ba*a?"
Output: Match

Code

Java

import java.util.Scanner;
public class WildcardMatch {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String t = sc.next(), p = sc.next();
        int m = t.length(), n = p.length();
        boolean[][] dp = new boolean[m + 1][n + 1];
        dp[0][0] = true;
        for (int j = 1; j <= n; j++) if (p.charAt(j-1) == '*') dp[0][j] = dp[0][j-1];
        for (int i = 1; i <= m; i++)
            for (int j = 1; j <= n; j++) {
                if (p.charAt(j-1) == '*') dp[i][j] = dp[i-1][j] || dp[i][j-1];
                else if (p.charAt(j-1) == '?' || t.charAt(i-1) == p.charAt(j-1)) dp[i][j] = dp[i-1][j-1];
            }
        System.out.println(dp[m][n] ? "Match" : "No Match");
    }
}

Python

t, p = input().split()
m, n = len(t), len(p)
dp = [[False] * (n + 1) for _ in range(m + 1)]
dp[0][0] = True
for j in range(1, n + 1):
    if p[j-1] == '*': dp[0][j] = dp[0][j-1]
for i in range(1, m + 1):
    for j in range(1, n + 1):
        if p[j-1] == '*': dp[i][j] = dp[i-1][j] or dp[i][j-1]
        elif p[j-1] == '?' or t[i-1] == p[j-1]: dp[i][j] = dp[i-1][j-1]
print("Match" if dp[m][n] else "No Match")

Time: O(M * N)Space: O(M * N)

Question 88

Maximum Occurring Character in a String

Problem

Find the character that occurs the most in a string.

Example:

Input: "programming"
Output: g

Code

Java

import java.util.Scanner;
public class MaxOccurringChar {
    public static void main(String[] args) {
        String s = new Scanner(System.in).next();
        int[] freq = new int[256];
        for (char c : s.toCharArray()) freq[c]++;
        int max = 0; char result = s.charAt(0);
        for (char c : s.toCharArray()) if (freq[c] > max) { max = freq[c]; result = c; }
        System.out.println(result);
    }
}

Python

from collections import Counter
print(Counter(input()).most_common(1)[0][0])

Time: O(N)Space: O(1)

Question 89

Remove All Duplicates from a String

Problem

Remove duplicate characters keeping only the first occurrence.

Example:

Input: "programming"
Output: "progamin"

Code

Java

import java.util.*;
public class RemoveDuplicateChars {
    public static void main(String[] args) {
        String s = new Scanner(System.in).next();
        Set<Character> seen = new LinkedHashSet<>();
        for (char c : s.toCharArray()) seen.add(c);
        StringBuilder sb = new StringBuilder();
        for (char c : seen) sb.append(c);
        System.out.println(sb);
    }
}

Python

print(''.join(dict.fromkeys(input())))

Time: O(N)Space: O(1)

Question 90

Print All Duplicates in a String

Problem

Print all characters that appear more than once with their count.

Example:

Input: "programming"
Output: r->2, g->2, m->2

Code

Java

import java.util.*;
public class PrintDuplicates {
    public static void main(String[] args) {
        String s = new Scanner(System.in).next();
        Map<Character, Integer> freq = new LinkedHashMap<>();
        for (char c : s.toCharArray()) freq.put(c, freq.getOrDefault(c, 0) + 1);
        for (Map.Entry<Character, Integer> e : freq.entrySet())
            if (e.getValue() > 1) System.out.println(e.getKey() + " -> " + e.getValue());
    }
}

Python

from collections import Counter
for ch, cnt in Counter(input()).items():
    if cnt > 1: print(f"{ch} -> {cnt}")

Time: O(N)Space: O(1)

Question 91

Remove Characters from First String Present in Second

Problem

Remove all characters from s1 that are present in s2.

Example:

Input: s1 = "hello world", s2 = "low"
Output: "he rd"

Code

Java

import java.util.*;
public class RemoveCharsFromFirst {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s1 = sc.nextLine(), s2 = sc.nextLine();
        Set<Character> remove = new HashSet<>();
        for (char c : s2.toCharArray()) remove.add(c);
        StringBuilder sb = new StringBuilder();
        for (char c : s1.toCharArray()) if (!remove.contains(c)) sb.append(c);
        System.out.println(sb);
    }
}

Python

s1 = input()
s2 = input()
print(''.join(c for c in s1 if c not in set(s2)))

Time: O(N + M)Space: O(M)

Question 92

Change Every Letter to Next Lexicographic Alphabet

Problem

Replace every letter with the next letter in alphabet (z wraps to a).

Example:

Input: "hello"
Output: "ifmmp"

Code

Java

import java.util.Scanner;
public class NextAlphabet {
    public static void main(String[] args) {
        String s = new Scanner(System.in).next();
        StringBuilder sb = new StringBuilder();
        for (char c : s.toCharArray()) {
            if (Character.isLetter(c)) {
                char base = Character.isUpperCase(c) ? 'A' : 'a';
                sb.append((char)(base + (c - base + 1) % 26));
            } else sb.append(c);
        }
        System.out.println(sb);
    }
}

Python

s = input()
result = ''
for c in s:
    if c.isalpha():
        base = ord('A') if c.isupper() else ord('a')
        result += chr(base + (ord(c) - base + 1) % 26)
    else: result += c
print(result)

Time: O(N)Space: O(N)

Question 93

Find the Largest Word in a String

Problem

Find the longest word in a sentence.

Example:

Input: "I love programming very much"
Output: "programming"

Code

Java

import java.util.Scanner;
public class LargestWord {
    public static void main(String[] args) {
        String[] words = new Scanner(System.in).nextLine().split(" ");
        String longest = "";
        for (String w : words) if (w.length() > longest.length()) longest = w;
        System.out.println(longest);
    }
}

Python

print(max(input().split(), key=len))

Time: O(N)Space: O(N)

Question 94

Sort Characters in a String

Problem

Sort characters of a string in alphabetical order.

Example:

Input: "programming"
Output: "aggimmnoprrr"

Code

Java

import java.util.*;
public class SortString {
    public static void main(String[] args) {
        char[] arr = new Scanner(System.in).next().toCharArray();
        Arrays.sort(arr);
        System.out.println(new String(arr));
    }
}

Python

print(''.join(sorted(input())))

Time: O(N log N)Space: O(N)

Question 95

Count Number of Words in a String

Problem

Count the number of words in a string.

Example:

Input: "Hello World This is Test"
Output: 5

Code

Java

import java.util.Scanner;
public class WordCount {
    public static void main(String[] args) {
        String s = new Scanner(System.in).nextLine().trim();
        System.out.println(s.isEmpty() ? 0 : s.split("\\s+").length);
    }
}

Python

print(len(input().split()))

Time: O(N)Space: O(N)

Question 96

Find Word with Highest Repeated Letters

Problem

Find the word that has the highest count of any repeated letter.

Example:

Input: "aabbbcc programming"
Output: "aabbbcc"

Code

Java

import java.util.*;
public class MostRepeatedLettersWord {
    public static void main(String[] args) {
        String[] words = new Scanner(System.in).nextLine().split(" ");
        String best = ""; int maxRepeat = 0;
        for (String w : words) {
            int[] freq = new int[256];
            for (char c : w.toCharArray()) freq[c]++;
            int localMax = 0;
            for (int f : freq) if (f > localMax) localMax = f;
            if (localMax > maxRepeat) { maxRepeat = localMax; best = w; }
        }
        System.out.println(best);
    }
}

Python

print(max(input().split(), key=lambda w: max(w.count(c) for c in set(w))))

Time: O(N)Space: O(1)

Question 97

Change Case of Each Character

Problem

Toggle the case of each character (uppercase to lowercase and vice versa).

Example:

Input: "Hello World"
Output: "hELLO wORLD"

Code

Java

import java.util.Scanner;
public class ChangeCase {
    public static void main(String[] args) {
        String s = new Scanner(System.in).nextLine();
        StringBuilder sb = new StringBuilder();
        for (char c : s.toCharArray())
            sb.append(Character.isUpperCase(c) ? Character.toLowerCase(c) : Character.toUpperCase(c));
        System.out.println(sb);
    }
}

Python

print(input().swapcase())

Time: O(N)Space: O(N)

Question 98

Concatenate One String to Another

Problem

Concatenate two strings without using built-in concatenation.

Example:

Input: s1 = "Hello", s2 = " World"
Output: "Hello World"

Code

Java

import java.util.Scanner;
public class ConcatStrings {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s1 = sc.nextLine(), s2 = sc.nextLine();
        char[] result = new char[s1.length() + s2.length()];
        int idx = 0;
        for (char c : s1.toCharArray()) result[idx++] = c;
        for (char c : s2.toCharArray()) result[idx++] = c;
        System.out.println(new String(result));
    }
}

Python

s1 = input()
s2 = input()
result = ''
for c in s1: result += c
for c in s2: result += c
print(result)

Time: O(N + M)Space: O(N + M)

Question 99

Find a Substring and Display Starting Position

Problem

Find a substring within a string and display its starting index.

Example:

Input: s = "Hello World", sub = "World"
Output: 6

Code

Java

import java.util.Scanner;
public class FindSubstring {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine(), sub = sc.nextLine();
        System.out.println(s.indexOf(sub));
    }
}

Python

s = input()
sub = input()
print(s.find(sub))

Time: O(N * M)Space: O(1)

Question 100

Reverse Words in a String

Problem

Reverse the order of words in a sentence.

Example:

Input: "Hello World Program"
Output: "Program World Hello"

Code

Java

import java.util.Scanner;
public class ReverseWords {
    public static void main(String[] args) {
        String[] words = new Scanner(System.in).nextLine().split(" ");
        StringBuilder sb = new StringBuilder();
        for (int i = words.length - 1; i >= 0; i--) {
            sb.append(words[i]);
            if (i > 0) sb.append(" ");
        }
        System.out.println(sb);
    }
}

Python

print(' '.join(input().split()[::-1]))

Time: O(N)Space: O(N)

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