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Practice Questions

Practice58 questions

Question 1

Work and Production Rate

Problem

A factory produces x units of a product in 24 days. How many units will it produce in 15 days?

Solution

Let the rate of production be R units per day.
R = x/24 (units per day)

Units produced in 15 days = R × 15 = (x/24) × 15 = 15x/24 = 5x/8

Question 2

Discount and Profit

Problem

A man buys a shirt at a discount of 25% on its marked price and sells it at a profit of 20% on its marked price. If the marked price is $400, what is the selling price of the shirt?

Solution

Marked Price = $400 Discount = 25% of$ 400 = (25/100) × 400 = $100 Buying Price = 400 - 100 =$ 300

Profit = 20% of $400 = (20/100) × 400 =$ 80
Selling Price = Buying Price + Profit = 300 + 80 = $380

Question 3

Volume of a Cube

Problem

If a cube has a volume of 512 cubic centimeters, what is the length of its side?

Solution

Volume of a cube = side × side × side
512 = side³
side = ∛512 = 8

Question 4

Average Speed

Problem

If a car travels a distance of 240 km with a speed of 60 km/h for the first 4 hours and then with a speed of 40 km/h for the next 3 hours, what is the average speed of the car for the entire journey?

Solution

Total distance traveled = 240 km
Total time taken = 4 hours + 3 hours = 7 hours
Average speed = Total distance / Total time = 240/7 ≈ 34.29 km/h

Question 5

Profit Percentage

Problem

If the cost price of an item is $200 and the selling price is$ 250, what is the profit percentage?

Solution

Profit = Selling Price - Cost Price = 250 - 200 = $50
Profit % = (Profit/Cost Price) × 100 = (50/200) × 100 = 25%

Question 6

Simplification

Problem

Simplify the following expression: (8 × 4 + 6) / 2 - 5

Solution

(8 × 4 + 6) / 2 - 5
= (32 + 6) / 2 - 5
= 38 / 2 - 5
= 19 - 5
= 14

Question 7

Linear Equation

Problem

Find the value of 'x' in the equation: 3x + 10 = 31

Solution

3x + 10 = 31
3x = 21
x = 7

Question 8

Discounted Price

Problem

A bookstore gives a 15% discount on all books. If the original price of a book is $40, what will be the discounted price?

Solution

Discounted price = Original price - (Original price × Discount percentage)
Discounted price = 40 - (40 × 0.15) = 40 - 6 = $34

Question 9

Consecutive Odd Numbers

Problem

The sum of two consecutive odd numbers is 64. What are the numbers?

Solution

Let the first odd number be x, the next is (x + 2).
x + (x + 2) = 64
2x + 2 = 64
2x = 62
x = 31

Question 10

Time to Cover Distance

Problem

A train travels a distance of 240 km at a constant speed of 60 km/h. How much time will it take to cover the distance?

Solution

Time = Distance / Speed = 240/60 = 4 hours

Question 11

Synonym

Problem

Choose the correct synonym for the word "Ephemeral": (a) Permanent (b) Fleeting (c) Eternal (d) Prolonged

Solution

"Ephemeral" means lasting for a very short time, which is closest in meaning to "Fleeting".

Question 12

Spelling

Problem

Identify the correctly spelled word: (a) Exaggerrate (b) Exagerate (c) Exaggerate (d) Exaggarate

Solution

The correct spelling is "Exaggerate" (double 'g', single 'r').

Question 13

Subject-Verb Agreement

Problem

Choose the sentence with correct subject-verb agreement:
(a) The group of students has started their project.
(b) The group of students have started their project.
(c) The group of students is starting their project.
(d) The group of students are starting their project.

Solution

"The group" is a singular collective noun and takes a singular verb.

Question 14

Fill in the Blank

Problem

He was _____ tired that he fell asleep immediately. (a) Too (b) Two (c) To (d) 2

Solution

"Too" is used to indicate excess ("too tired"), fitting the sentence's meaning.

Question 15

Use of Articles

Problem

Identify the correct sentence with the use of articles:
(a) I have a apple.
(b) I have an apple.
(c) I have the apple.
(d) I have apple.

Solution

"Apple" begins with a vowel sound, so it takes the article "an".

Question 16

Number Series

Problem

Choose the next number in the series: 2, 5, 11, 20, ?

Solution

The series adds consecutive multiples of 3 (odd increments of the differences):
2 + 3 = 5
5 + 6 = 11
11 + 9 = 20
20 + 12 = 32

Question 17

Coding-Decoding

Problem

If APPLE is coded as 116165 (using alphabet positions), how is ORANGE coded?

Solution

Each letter is replaced by its position in the English alphabet:
A=1, P=16, P=16, L=12, E=5

Using the same scheme for ORANGE:
O=15, R=18, A=1, N=14, G=7, E=5

Question 18

Odd One Out

Problem

Which word does not belong to the group? (a) Square (b) Circle (c) Rectangle (d) Triangle

Solution

Square, Rectangle, and Triangle are shapes made of straight lines, while a Circle is a curved shape.

Question 19

Letter Coding

Problem

If CAT is coded as 3-1-20, DOG is coded as 4-15-7, how is FISH coded?

Solution

Each letter is replaced by its position in the alphabet:
C=3, A=1, T=20 → CAT = 3-1-20
D=4, O=15, G=7 → DOG = 4-15-7

For FISH: F=6, I=9, S=19, H=8

Question 20

Alphabetical Ordering

Problem

Arrange the following words in alphabetical order: Monitor, Apple, Keyboard, Mouse

Solution

Comparing first letters: A < K < M(onitor) < M(ouse)
Apple, Keyboard, Monitor, Mouse

Question 21

Second Largest Element in an Array

Problem

Write a program to find the second largest number in an array.

Example:

Input: [12, 35, 1, 10, 34, 1]
Output: 34

Code

Java

public class SecondLargestInArray {
    public static void main(String[] args) {
        int[] arr = {12, 35, 1, 10, 34, 1};
        int largest = arr[0];
        int secondLargest = arr[0];
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] > largest) {
                secondLargest = largest;
                largest = arr[i];
            } else if (arr[i] > secondLargest && arr[i] != largest) {
                secondLargest = arr[i];
            }
        }
        System.out.println("The second largest element is: " + secondLargest);
    }
}

Python

arr = [12, 35, 1, 10, 34, 1]
largest = second_largest = arr[0]
for num in arr:
    if num > largest:
        second_largest = largest
        largest = num
    elif num > second_largest and num != largest:
        second_largest = num
print("The second largest element is:", second_largest)

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

Question 22

Reverse an Array In-Place

Problem

Write a program to reverse an array in-place.

Example:

Input: [10, 20, 30, 40, 50]
Output: [50, 40, 30, 20, 10]

Code

Java

import java.util.Arrays;
public class ReverseArray {
    public static void main(String[] args) {
        int[] arr = {10, 20, 30, 40, 50};
        int start = 0, end = arr.length - 1;
        while (start < end) {
            int temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;
            start++;
            end--;
        }
        System.out.println("Reversed array is: " + Arrays.toString(arr));
    }
}

Python

arr = [10, 20, 30, 40, 50]
start, end = 0, len(arr) - 1
while start < end:
    arr[start], arr[end] = arr[end], arr[start]
    start += 1
    end -= 1
print("Reversed array is:", arr)

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

Question 23

Find Duplicate Elements in an Array

Problem

Write a program to find the duplicate values in an array of integers.

Example:

Input: [10, 20, 20, 30, 30, 30, 40, 50, 50]
Output: 20 30 30 50

Code

Java

public class FindDuplicates {
    public static void main(String[] args) {
        int[] arr = {10, 20, 20, 30, 30, 30, 40, 50, 50};
        System.out.println("Duplicate elements in array are: ");
        for (int i = 0; i < arr.length; i++) {
            for (int j = i + 1; j < arr.length; j++) {
                if (arr[i] == arr[j]) {
                    System.out.println(arr[j]);
                }
            }
        }
    }
}

Python

arr = [10, 20, 20, 30, 30, 30, 40, 50, 50]
print("Duplicate elements in array are:")
for i in range(len(arr)):
    for j in range(i + 1, len(arr)):
        if arr[i] == arr[j]:
            print(arr[j])

Time: O(N²)Space: O(1)

Question 24

Count Even and Odd Integers

Problem

Write a program to find the number of even and odd integers in a given array of integers.

Example:

Input: [10, 20, 21, 30, 31, 40, 41]
Output: Even: 4, Odd: 3

Code

Java

public class CountEvenOdd {
    public static void main(String[] args) {
        int[] arr = {10, 20, 21, 30, 31, 40, 41};
        int even = 0, odd = 0;
        for (int num : arr) {
            if (num % 2 == 0) even++;
            else odd++;
        }
        System.out.println("Number of even elements: " + even);
        System.out.println("Number of odd elements: " + odd);
    }
}

Python

arr = [10, 20, 21, 30, 31, 40, 41]
even = sum(1 for num in arr if num % 2 == 0)
odd = len(arr) - even
print("Number of even elements:", even)
print("Number of odd elements:", odd)

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

Question 25

Common Elements Between Two Sorted Arrays

Problem

Write a program to find the common elements between two arrays of sorted elements.

Example:

Input: arr1 = [1, 3, 4, 5, 7], arr2 = [2, 3, 5, 6]
Output: 3 5

Code

Java

public class CommonElements {
    public static void main(String[] args) {
        int[] arr1 = {1, 3, 4, 5, 7};
        int[] arr2 = {2, 3, 5, 6};
        System.out.println("Common elements are: ");
        for (int i = 0; i < arr1.length; i++) {
            for (int j = 0; j < arr2.length; j++) {
                if (arr1[i] == arr2[j]) {
                    System.out.println(arr1[i]);
                }
            }
        }
    }
}

Python

arr1 = [1, 3, 4, 5, 7]
arr2 = [2, 3, 5, 6]
print("Common elements are:")
for num in arr1:
    if num in arr2:
        print(num)

Time: O(N×M)Space: O(1)

Question 26

Palindrome Check

Problem

Write a program to check whether a given string is a palindrome or not.

Example:

Input: "madam"
Output: madam is a palindrome

Code

Java

public class Palindrome {
    public static void main(String[] args) {
        String str = "madam";
        String reversed = new StringBuilder(str).reverse().toString();
        if (str.equals(reversed)) {
            System.out.println(str + " is a palindrome");
        } else {
            System.out.println(str + " is not a palindrome");
        }
    }
}

Python

str_val = "madam"
if str_val == str_val[::-1]:
    print(str_val, "is a palindrome")
else:
    print(str_val, "is not a palindrome")

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

Question 27

Reverse Words in a Sentence

Problem

Write a program to reverse the words in a given sentence without using any library method.

Example:

Input: "Hello World"
Output: "olleH dlroW "

Code

Java

public class ReverseWords {
    public static void main(String[] args) {
        String str = "Hello World";
        String[] words = str.split(" ");
        String reversedString = "";
        for (String word : words) {
            String reversedWord = "";
            for (int j = word.length() - 1; j >= 0; j--) {
                reversedWord = reversedWord + word.charAt(j);
            }
            reversedString = reversedString + reversedWord + " ";
        }
        System.out.println(reversedString);
    }
}

Python

str_val = "Hello World"
words = str_val.split(" ")
reversed_string = ""
for word in words:
    reversed_word = ""
    for ch in word:
        reversed_word = ch + reversed_word
    reversed_string += reversed_word + " "
print(reversed_string)

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

Question 28

Count Vowels and Consonants

Problem

Write a program to count the total number of vowels and consonants in a string.

Example:

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

Code

Java

public class CountVowelsConsonants {
    public static void main(String[] args) {
        String str = "Hello World";
        int vowels = 0, consonants = 0;
        for (int i = 0; i < str.length(); ++i) {
            char ch = Character.toLowerCase(str.charAt(i));
            if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
                ++vowels;
            } else if (ch >= 'a' && ch <= 'z') {
                ++consonants;
            }
        }
        System.out.println("Number of vowels: " + vowels);
        System.out.println("Number of consonants: " + consonants);
    }
}

Python

str_val = "Hello World"
vowels = consonants = 0
for ch in str_val.lower():
    if ch in "aeiou":
        vowels += 1
    elif ch.isalpha():
        consonants += 1
print("Number of vowels:", vowels)
print("Number of consonants:", consonants)

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

Question 29

Anagram Check

Problem

Write a program to check whether two strings are anagrams of each other.

Example:

Input: str1 = "Listen", str2 = "Silent"
Output: Listen and Silent are anagrams.

Code

Java

import java.util.Arrays;
public class AnagramCheck {
    public static void main(String[] args) {
        String str1 = "Listen".toLowerCase();
        String str2 = "Silent".toLowerCase();
        if (str1.length() == str2.length()) {
            char[] charArray1 = str1.toCharArray();
            char[] charArray2 = str2.toCharArray();
            Arrays.sort(charArray1);
            Arrays.sort(charArray2);
            boolean result = Arrays.equals(charArray1, charArray2);
            System.out.println(str1 + " and " + str2 + (result ? " are anagrams." : " are not anagrams."));
        } else {
            System.out.println(str1 + " and " + str2 + " are not anagrams.");
        }
    }
}

Python

str1 = "Listen".lower()
str2 = "Silent".lower()
if sorted(str1) == sorted(str2):
    print(str1, "and", str2, "are anagrams.")
else:
    print(str1, "and", str2, "are not anagrams.")

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

Question 30

Convert String to Lowercase

Problem

Write a program to convert a given string into lowercase.

Example:

Input: "HELLO WORLD"
Output: "hello world"

Code

Java

public class LowercaseString {
    public static void main(String[] args) {
        String str = "HELLO WORLD";
        str = str.toLowerCase();
        System.out.println("String in lowercase: " + str);
    }
}

Python

str_val = "HELLO WORLD"
print("String in lowercase:", str_val.lower())

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

Question 31

Fibonacci Series

Problem

Write a program to print the Fibonacci series up to n terms.

Example:

Input: n = 10
Output: 0 1 1 2 3 5 8 13 21 34

Code

Java

public class Fibonacci {
    public static void main(String[] args) {
        int n = 10;
        int t1 = 0, t2 = 1;
        System.out.print("First " + n + " terms: ");
        for (int i = 1; i <= n; ++i) {
            System.out.print(t1 + " ");
            int sum = t1 + t2;
            t1 = t2;
            t2 = sum;
        }
    }
}

Python

n = 10
t1, t2 = 0, 1
print(f"First {n} terms:", end=" ")
for _ in range(n):
    print(t1, end=" ")
    t1, t2 = t2, t1 + t2

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

Question 32

Prime Numbers up to N

Problem

Write a program to print all prime numbers up to n.

Example:

Input: n = 30
Output: 2 3 5 7 11 13 17 19 23 29

Code

Java

public class PrimeNumbers {
    public static void main(String[] args) {
        int n = 30;
        System.out.println("Prime numbers up to " + n);
        for (int i = 2; i <= n; i++) {
            if (isPrime(i)) System.out.print(i + " ");
        }
    }

    public static boolean isPrime(int num) {
        if (num <= 1) return false;
        for (int i = 2; i < num; i++) {
            if (num % i == 0) return false;
        }
        return true;
    }
}

Python

def is_prime(num):
    if num <= 1:
        return False
    for i in range(2, num):
        if num % i == 0:
            return False
    return True

n = 30
print(f"Prime numbers up to {n}")
print(" ".join(str(i) for i in range(2, n + 1) if is_prime(i)))

Time: O(N²)Space: O(1)

Question 33

Armstrong Numbers

Problem

Write a program to print the Armstrong numbers between 1 and n.

Example:

Input: n = 500
Output: 1 153 370 371 407

Code

Java

public class ArmstrongNumbers {
    public static void main(String[] args) {
        int n = 500;
        for (int i = 1; i <= n; i++) {
            if (isArmstrong(i)) System.out.print(i + " ");
        }
    }

    public static boolean isArmstrong(int num) {
        int original = num;
        int sum = 0;
        while (num != 0) {
            int digit = num % 10;
            sum += Math.pow(digit, 3);
            num /= 10;
        }
        return sum == original;
    }
}

Python

def is_armstrong(num):
    original = num
    total = sum(int(d) ** 3 for d in str(num))
    return total == original

n = 500
print(" ".join(str(i) for i in range(1, n + 1) if is_armstrong(i)))

Time: O(N × log N)Space: O(1)

Question 34

Pattern Series

Problem

Write a program to print the pattern series like 1, 12, 123, 1234, ..., up to n.

Example:

Input: n = 5
Output:
1
12
123
1234
12345

Code

Java

public class PatternSeries {
    public static void main(String[] args) {
        int n = 5;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= i; j++) {
                System.out.print(j);
            }
            System.out.println();
        }
    }
}

Python

n = 5
for i in range(1, n + 1):
    print("".join(str(j) for j in range(1, i + 1)))

Time: O(N²)Space: O(1)

Question 35

Sum of Harmonic Series

Problem

Write a program to print the sum of the series 1 + 1/2 + 1/3 + ... + 1/n.

Example:

Input: n = 5
Output: 2.2833333333333332

Code

Java

public class SeriesSum {
    public static void main(String[] args) {
        int n = 5;
        double result = 0.0;
        for (int i = 1; i <= n; i++) {
            result += 1.0 / i;
        }
        System.out.println("The sum of the series is " + result);
    }
}

Python

n = 5
result = sum(1.0 / i for i in range(1, n + 1))
print("The sum of the series is", result)

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

Question 36

Decimal to Binary

Problem

Write a program to convert a decimal number to binary.

Example:

Input: 10
Output: 1010

Code

Java

public class DecimalToBinary {
    public static void main(String[] args) {
        int num = 10;
        String binary = Integer.toBinaryString(num);
        System.out.println("Binary representation of " + num + " is " + binary);
    }
}

Python

num = 10
print(f"Binary representation of {num} is {bin(num)[2:]}")

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

Question 37

Binary to Decimal

Problem

Write a program to convert a binary number to decimal.

Example:

Input: "1010"
Output: 10

Code

Java

public class BinaryToDecimal {
    public static void main(String[] args) {
        String binary = "1010";
        int decimal = Integer.parseInt(binary, 2);
        System.out.println("Decimal representation of " + binary + " is " + decimal);
    }
}

Python

binary = "1010"
decimal = int(binary, 2)
print(f"Decimal representation of {binary} is {decimal}")

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

Question 38

Decimal to Hexadecimal

Problem

Write a program to convert a decimal number to hexadecimal.

Example:

Input: 255
Output: ff

Code

Java

public class DecimalToHexadecimal {
    public static void main(String[] args) {
        int num = 255;
        String hex = Integer.toHexString(num);
        System.out.println("Hexadecimal representation of " + num + " is " + hex);
    }
}

Python

num = 255
print(f"Hexadecimal representation of {num} is {hex(num)[2:]}")

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

Question 39

Fahrenheit to Celsius

Problem

Write a program to convert Fahrenheit to Celsius.

Example:

Input: 100.0
Output: 37.77777777777778

Code

Java

public class FahrenheitToCelsius {
    public static void main(String[] args) {
        double fahrenheit = 100.0;
        double celsius = (fahrenheit - 32) * 5 / 9;
        System.out.println(fahrenheit + " degree Fahrenheit is equal to " + celsius + " in Celsius");
    }
}

Python

fahrenheit = 100.0
celsius = (fahrenheit - 32) * 5 / 9
print(f"{fahrenheit} degree Fahrenheit is equal to {celsius} in Celsius")

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

Question 40

String to Integer Without parseInt

Problem

Write a program to convert a string to an integer without using Integer.parseInt().

Example:

Input: "123"
Output: 123

Code

Java

public class StringToInteger {
    public static void main(String[] args) {
        String str = "123";
        int num = 0;
        for (char c : str.toCharArray()) {
            num = num * 10 + (c - '0');
        }
        System.out.println("The integer value of " + str + " is " + num);
    }
}

Python

str_val = "123"
num = 0
for c in str_val:
    num = num * 10 + (ord(c) - ord('0'))
print(f"The integer value of {str_val} is {num}")

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

Question 41

Bubble Sort

Problem

Implement the bubble sort algorithm for a given array of integers.

Example:

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

Code

Java

import java.util.Arrays;
public class BubbleSort {
    public static void main(String[] args) {
        int[] array = {64, 34, 25, 12, 22, 11, 90};
        bubbleSort(array);
        System.out.println("Sorted array: " + Arrays.toString(array));
    }

    public static void bubbleSort(int[] array) {
        int n = array.length;
        for (int i = 0; i < n - 1; i++) {
            for (int j = 0; j < n - i - 1; j++) {
                if (array[j] > array[j + 1]) {
                    int temp = array[j];
                    array[j] = array[j + 1];
                    array[j + 1] = temp;
                }
            }
        }
    }
}

Python

def bubble_sort(array):
    n = len(array)
    for i in range(n - 1):
        for j in range(n - i - 1):
            if array[j] > array[j + 1]:
                array[j], array[j + 1] = array[j + 1], array[j]

array = [64, 34, 25, 12, 22, 11, 90]
bubble_sort(array)
print("Sorted array:", array)

Time: O(N²)Space: O(1)

Question 42

Insertion Sort

Problem

Implement the insertion sort algorithm for a given array of integers.

Example:

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

Code

Java

import java.util.Arrays;
public class InsertionSort {
    public static void main(String[] args) {
        int[] array = {12, 11, 13, 5, 6};
        insertionSort(array);
        System.out.println("Sorted array: " + Arrays.toString(array));
    }

    public static void insertionSort(int[] array) {
        int n = array.length;
        for (int i = 1; i < n; ++i) {
            int key = array[i];
            int j = i - 1;
            while (j >= 0 && array[j] > key) {
                array[j + 1] = array[j];
                j = j - 1;
            }
            array[j + 1] = key;
        }
    }
}

Python

def insertion_sort(array):
    for i in range(1, len(array)):
        key = array[i]
        j = i - 1
        while j >= 0 and array[j] > key:
            array[j + 1] = array[j]
            j -= 1
        array[j + 1] = key

array = [12, 11, 13, 5, 6]
insertion_sort(array)
print("Sorted array:", array)

Time: O(N²)Space: O(1)

Question 43

Selection Sort

Problem

Implement the selection sort algorithm for a given array of integers.

Example:

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

Code

Java

import java.util.Arrays;
public class SelectionSort {
    public static void main(String[] args) {
        int[] array = {64, 25, 12, 22, 11};
        selectionSort(array);
        System.out.println("Sorted array: " + Arrays.toString(array));
    }

    public static void selectionSort(int[] array) {
        int n = array.length;
        for (int i = 0; i < n - 1; i++) {
            int minIndex = i;
            for (int j = i + 1; j < n; j++) {
                if (array[j] < array[minIndex]) {
                    minIndex = j;
                }
            }
            int temp = array[minIndex];
            array[minIndex] = array[i];
            array[i] = temp;
        }
    }
}

Python

def selection_sort(array):
    n = len(array)
    for i in range(n - 1):
        min_index = i
        for j in range(i + 1, n):
            if array[j] < array[min_index]:
                min_index = j
        array[i], array[min_index] = array[min_index], array[i]

array = [64, 25, 12, 22, 11]
selection_sort(array)
print("Sorted array:", array)

Time: O(N²)Space: O(1)

Question 44

Quick Sort

Problem

Implement the quick sort algorithm for a given array of integers.

Example:

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

Code

Java

import java.util.Arrays;
public class QuickSort {
    public static void main(String[] args) {
        int[] array = {10, 7, 8, 9, 1, 5};
        quickSort(array, 0, array.length - 1);
        System.out.println("Sorted array: " + Arrays.toString(array));
    }

    public static int partition(int[] array, int low, int high) {
        int pivot = array[high];
        int i = low - 1;
        for (int j = low; j < high; j++) {
            if (array[j] < pivot) {
                i++;
                int temp = array[i];
                array[i] = array[j];
                array[j] = temp;
            }
        }
        int temp = array[i + 1];
        array[i + 1] = array[high];
        array[high] = temp;
        return i + 1;
    }

    public static void quickSort(int[] array, int low, int high) {
        if (low < high) {
            int pi = partition(array, low, high);
            quickSort(array, low, pi - 1);
            quickSort(array, pi + 1, high);
        }
    }
}

Python

def partition(array, low, high):
    pivot = array[high]
    i = low - 1
    for j in range(low, high):
        if array[j] < pivot:
            i += 1
            array[i], array[j] = array[j], array[i]
    array[i + 1], array[high] = array[high], array[i + 1]
    return i + 1

def quick_sort(array, low, high):
    if low < high:
        pi = partition(array, low, high)
        quick_sort(array, low, pi - 1)
        quick_sort(array, pi + 1, high)

array = [10, 7, 8, 9, 1, 5]
quick_sort(array, 0, len(array) - 1)
print("Sorted array:", array)

Time: O(N log N) averageSpace: O(log N)

Question 45

Merge Sort

Problem

Implement the merge sort algorithm for a given array of integers.

Example:

Input: [12, 11, 13, 5, 6, 7]
Output: [5, 6, 7, 11, 12, 13]

Code

Java

import java.util.Arrays;
public class MergeSort {
    public static void main(String[] args) {
        int[] array = {12, 11, 13, 5, 6, 7};
        mergeSort(array, 0, array.length - 1);
        System.out.println("Sorted array: " + Arrays.toString(array));
    }

    public static void mergeSort(int[] array, int left, int right) {
        if (left < right) {
            int mid = (left + right) / 2;
            mergeSort(array, left, mid);
            mergeSort(array, mid + 1, right);
            merge(array, left, mid, right);
        }
    }

    public static void merge(int[] array, int left, int mid, int right) {
        int n1 = mid - left + 1;
        int n2 = right - mid;
        int[] leftArr = new int[n1];
        int[] rightArr = new int[n2];
        for (int i = 0; i < n1; ++i) leftArr[i] = array[left + i];
        for (int j = 0; j < n2; ++j) rightArr[j] = array[mid + 1 + j];

        int i = 0, j = 0, k = left;
        while (i < n1 && j < n2) {
            if (leftArr[i] <= rightArr[j]) array[k++] = leftArr[i++];
            else array[k++] = rightArr[j++];
        }
        while (i < n1) array[k++] = leftArr[i++];
        while (j < n2) array[k++] = rightArr[j++];
    }
}

Python

def merge_sort(array):
    if len(array) > 1:
        mid = len(array) // 2
        left, right = array[:mid], array[mid:]
        merge_sort(left)
        merge_sort(right)

        i = j = k = 0
        while i < len(left) and j < len(right):
            if left[i] <= right[j]:
                array[k] = left[i]
                i += 1
            else:
                array[k] = right[j]
                j += 1
            k += 1
        while i < len(left):
            array[k] = left[i]
            i += 1
            k += 1
        while j < len(right):
            array[k] = right[j]
            j += 1
            k += 1

array = [12, 11, 13, 5, 6, 7]
merge_sort(array)
print("Sorted array:", array)

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

Question 46

Towers of Hanoi

Problem

Write a program to solve the Towers of Hanoi problem with 'n' disks.

Example:

Input: n = 3
Output: Sequence of moves to transfer 3 disks from rod A to rod C using rod B

Code

Java

public class TowersOfHanoi {
    public static void main(String[] args) {
        int n = 3;
        towerOfHanoi(n, 'A', 'C', 'B');
    }

    static void towerOfHanoi(int n, char fromRod, char toRod, char auxRod) {
        if (n == 1) {
            System.out.println("Move disk 1 from rod " + fromRod + " to rod " + toRod);
            return;
        }
        towerOfHanoi(n - 1, fromRod, auxRod, toRod);
        System.out.println("Move disk " + n + " from rod " + fromRod + " to rod " + toRod);
        towerOfHanoi(n - 1, auxRod, toRod, fromRod);
    }
}

Python

def tower_of_hanoi(n, from_rod, to_rod, aux_rod):
    if n == 1:
        print(f"Move disk 1 from rod {from_rod} to rod {to_rod}")
        return
    tower_of_hanoi(n - 1, from_rod, aux_rod, to_rod)
    print(f"Move disk {n} from rod {from_rod} to rod {to_rod}")
    tower_of_hanoi(n - 1, aux_rod, to_rod, from_rod)

tower_of_hanoi(3, 'A', 'C', 'B')

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

Question 47

Longest Common Subsequence (LCS)

Problem

Write a program to find the Longest Common Subsequence (LCS) in two strings.

Example:

Input: s1 = "AGGTAB", s2 = "GXTXAYB"
Output: 4

Code

Java

public class LCS {
    public static void main(String[] args) {
        String s1 = "AGGTAB";
        String s2 = "GXTXAYB";
        int result = lcs(s1, s2, s1.length(), s2.length());
        System.out.println("Length of LCS is " + result);
    }

    static int lcs(String s1, String s2, int m, int n) {
        if (m == 0 || n == 0) return 0;
        if (s1.charAt(m - 1) == s2.charAt(n - 1)) return 1 + lcs(s1, s2, m - 1, n - 1);
        else return Math.max(lcs(s1, s2, m, n - 1), lcs(s1, s2, m - 1, n));
    }
}

Python

def lcs(s1, s2, m, n):
    if m == 0 or n == 0:
        return 0
    if s1[m - 1] == s2[n - 1]:
        return 1 + lcs(s1, s2, m - 1, n - 1)
    return max(lcs(s1, s2, m, n - 1), lcs(s1, s2, m - 1, n))

s1, s2 = "AGGTAB", "GXTXAYB"
print("Length of LCS is", lcs(s1, s2, len(s1), len(s2)))

Time: O(2^N) naive recursion (O(M×N) with DP memoization)Space: O(M+N) recursion stack

Question 48

All Permutations of a String

Problem

Write a program to find all permutations of a string.

Example:

Input: "ABC"
Output: ABC ACB BAC BCA CBA CAB

Code

Java

public class StringPermutation {
    public static void main(String[] args) {
        String str = "ABC";
        int n = str.length();
        permute(str, 0, n - 1);
    }

    private static void permute(String str, int l, int r) {
        if (l == r) {
            System.out.println(str);
        } else {
            for (int i = l; i <= r; i++) {
                str = swap(str, l, i);
                permute(str, l + 1, r);
                str = swap(str, l, i);
            }
        }
    }

    public static String swap(String a, int i, int j) {
        char[] charArray = a.toCharArray();
        char temp = charArray[i];
        charArray[i] = charArray[j];
        charArray[j] = temp;
        return String.valueOf(charArray);
    }
}

Python

from itertools import permutations

str_val = "ABC"
for p in permutations(str_val):
    print("".join(p))

Time: O(N × N!)Space: O(N)

Question 49

Breadth-First Search (BFS)

Problem

Write an algorithm to implement breadth-first search (BFS) for a graph.

Code

Python

def bfs(graph, start):
    visited = []
    queue = [start]
    visited.append(start)
    while queue:
        m = queue.pop(0)
        print(m, end=" ")
        for neighbour in graph[m]:
            if neighbour not in visited:
                visited.append(neighbour)
                queue.append(neighbour)

Time: O(V + E)Space: O(V)

Question 50

Depth-First Search (DFS)

Problem

Write an algorithm to implement depth-first search (DFS) for a graph.

Code

Python

def dfs(graph, start, visited=None):
    if visited is None:
        visited = set()
    visited.add(start)
    print(start, end=" ")
    for next_node in graph[start] - visited:
        dfs(graph, next_node, visited)
    return visited

Time: O(V + E)Space: O(V)

Question 51

Heap Sort

Problem

Implement an algorithm to sort an array using the heap sort method.

Code

Python

def heapify(arr, n, i):
    largest = i
    l = 2 * i + 1
    r = 2 * i + 2
    if l < n and arr[i] < arr[l]:
        largest = l
    if r < n and arr[largest] < arr[r]:
        largest = r
    if largest != i:
        arr[i], arr[largest] = arr[largest], arr[i]
        heapify(arr, n, largest)

def heap_sort(arr):
    n = len(arr)
    for i in range(n // 2 - 1, -1, -1):
        heapify(arr, n, i)
    for i in range(n - 1, 0, -1):
        arr[i], arr[0] = arr[0], arr[i]
        heapify(arr, i, 0)

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

Question 52

Dijkstra's Algorithm

Problem

Write a program to find the shortest path between two nodes in a weighted graph using Dijkstra's Algorithm.

Code

Python

def dijkstra(graph, start_vertex):
    D = {v: float('infinity') for v in graph}
    D[start_vertex] = 0
    unseen_nodes = list(graph)

    while unseen_nodes:
        min_node = None
        for node in unseen_nodes:
            if min_node is None or D[node] < D[min_node]:
                min_node = node

        for neighbour, weight in graph[min_node].items():
            if weight + D[min_node] < D[neighbour]:
                D[neighbour] = weight + D[min_node]

        unseen_nodes.remove(min_node)

    return D

Time: O(V²) with an array-based implementationSpace: O(V)

Question 53

Binary Tree Traversals

Problem

Write a program to find the InOrder, PreOrder, and PostOrder traversal of a Binary Tree.

Code

Python

class Node:
    def __init__(self, key):
        self.left = None
        self.right = None
        self.val = key

def print_inorder(root):
    if root:
        print_inorder(root.left)
        print(root.val, end=" ")
        print_inorder(root.right)

def print_postorder(root):
    if root:
        print_postorder(root.left)
        print_postorder(root.right)
        print(root.val, end=" ")

def print_preorder(root):
    if root:
        print(root.val, end=" ")
        print_preorder(root.left)
        print_preorder(root.right)

Time: O(N) for each traversalSpace: O(H) where H is tree height (recursion stack)

Question 54

Encapsulation

Problem

Explain the concept of encapsulation with a coding example.

Solution

Encapsulation is one of the four fundamental OOP concepts (alongside inheritance, polymorphism, and abstraction). It is the mechanism of wrapping data (variables) and the code acting on that data (methods) together as a single unit, hiding the variables from other classes and exposing them only through methods — also known as data hiding.

Code

Java

public class Employee {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String newName) {
        name = newName;
    }
}

Question 55

Polymorphism

Problem

Write a program to implement polymorphism in Java.

Solution

Polymorphism allows performing a single action in different ways — one interface, multiple implementations.

Code

Java

class Animal {
    public void animalSound() {
        System.out.println("The animal makes a sound");
    }
}

class Pig extends Animal {
    public void animalSound() {
        System.out.println("The pig says: wee wee");
    }
}

class Dog extends Animal {
    public void animalSound() {
        System.out.println("The dog says: bow wow");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myAnimal = new Animal();
        Animal myPig = new Pig();
        Animal myDog = new Dog();
        myAnimal.animalSound();
        myPig.animalSound();
        myDog.animalSound();
    }
}

Question 56

Overloading vs Overriding

Problem

What is the difference between overloading and overriding? Provide a code example.

Solution

Overloading is defining multiple methods with the same name but different parameters within the same class. Overriding is when a subclass provides a specific implementation of a method already defined in its superclass.

Code

Java

// Overloading example
public class DemoClass {
    void demoMethod(int i) {
        System.out.println("Method with int: " + i);
    }
    void demoMethod(double d) {
        System.out.println("Method with double: " + d);
    }
}

// Overriding example
class Animal {
    void eat() {
        System.out.println("eating...");
    }
}

class Dog extends Animal {
    void eat() {
        System.out.println("eating bread...");
    }
}

Question 57

Inheritance

Problem

Explain the concept of inheritance with an example. What are the different types of inheritance supported in Java and C++?

Solution

Inheritance allows a class to inherit the properties (fields) and methods of another class. The class being inherited from is the parent (base) class, and the class inheriting is the child (derived) class.

Code

Java

class Bicycle {
    public int gear;
    public int speed;

    public Bicycle(int gear, int speed) {
        this.gear = gear;
        this.speed = speed;
    }

    public void applyBrake(int decrement) {
        speed -= decrement;
    }

    public void speedUp(int increment) {
        speed += increment;
    }
}

class MountainBike extends Bicycle {
    public int seatHeight;

    public MountainBike(int gear, int speed, int startHeight) {
        super(gear, speed);
        seatHeight = startHeight;
    }

    public void setHeight(int newValue) {
        seatHeight = newValue;
    }
}

Question 58

Interfaces

Problem

Write a program to implement an interface in Java. Also explain the difference between a class and an interface.

Solution

An interface is a blueprint of a class containing only static constants and abstract methods (no method bodies), used to achieve full abstraction and multiple inheritance in Java.

Code

Java

interface Animal {
    void eat();
    void sound();
}

class Cat implements Animal {
    public void eat() {
        System.out.println("Cat eats");
    }
    public void sound() {
        System.out.println("Cat meows");
    }
}

public class Main {
    public static void main(String[] args) {
        Cat c1 = new Cat();
        c1.eat();
        c1.sound();
    }
}

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