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LTIMindtree

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Practice Questions

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Question 1

Longest Common Subsequence of Vowels Only

Problem

Given two strings, find the length of the longest common subsequence which contains only vowels.

Example:

Input: input1 = "vowelpunish", input2 = "english"
Output: 2

Input: input1 = "prepinsta", input2 = "prepare"
Output: 2

Code

Java

public class VowelLCS {
    static boolean isVowel(char c) {
        return "aeiouAEIOU".indexOf(c) != -1;
    }

    public static int vowelLCS(String s1, String s2) {
        int m = s1.length(), n = s2.length();
        int[][] dp = new int[m + 1][n + 1];
        for (int i = 1; i <= m; i++) {
            for (int j = 1; j <= n; j++) {
                if (s1.charAt(i - 1) == s2.charAt(j - 1) && isVowel(s1.charAt(i - 1))) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                } else {
                    dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
                }
            }
        }
        return dp[m][n];
    }

    public static void main(String[] args) {
        System.out.println(vowelLCS("vowelpunish", "english"));
    }
}

Time: O(M×N)Space: O(M×N)

Question 2

Longest Decreasing Subsequence

Problem

Given N tokens arranged in a line with numbers written on them, find the length of the longest decreasing subsequence.

Example:

Input: n = 5, A = [5, 0, 3, 2, 9]
Output: 3
Explanation: The longest decreasing subsequence is [5, 3, 2]

Input: n = 9, A = [15, 27, 14, 38, 63, 55, 46, 65, 85]
Output: 3
Explanation: The longest decreasing subsequence is [63, 55, 46]

Code

Java

public class LongestDecreasingSubsequence {
    public static int longestDecreasingSubsequence(int[] arr) {
        int n = arr.length;
        int[] dp = new int[n];
        java.util.Arrays.fill(dp, 1);
        int maxLen = 1;
        for (int i = 1; i < n; i++) {
            for (int j = 0; j < i; j++) {
                if (arr[i] < arr[j]) {
                    dp[i] = Math.max(dp[i], dp[j] + 1);
                }
            }
            maxLen = Math.max(maxLen, dp[i]);
        }
        return maxLen;
    }

    public static void main(String[] args) {
        System.out.println(longestDecreasingSubsequence(new int[]{5, 0, 3, 2, 9}));
    }
}

Time: O(N²)Space: O(N)

Question 3

Minimum Penalty (Sum of Absolute Differences)

Problem

Maxwell filled his exam form with subject marks swapped by mistake. He wants to update his marks, but must pay a penalty equal to the sum of absolute differences between adjacent subject marks. Return the minimum penalty.

Example:

Input: arr = [5, 10, 1, 4, 8, 7]
Output: 9

Input: arr = [12, 10, 15, 22, 21, 20, 1, 8, 9]
Output: 18

Code

Java

public class MinPenalty {
    public static int minPenalty(int[] arr) {
        int penalty = 0;
        for (int i = 1; i < arr.length; i++) {
            penalty += Math.abs(arr[i] - arr[i - 1]);
        }
        return penalty;
    }

    public static void main(String[] args) {
        System.out.println(minPenalty(new int[]{5, 10, 1, 4, 8, 7}));
    }
}

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

Question 4

Maximum Difference with Larger Element Appearing After

Problem

Given an array, find the maximum difference between two elements such that the larger element appears after the smaller one.

Example:

Input: arr = [2, 3, 10, 6, 4, 8, 1]
Output: 8
Explanation: The maximum difference is between 10 and 2.

Input: arr = [7, 9, 5, 6, 3, 2]
Output: 2
Explanation: The maximum difference is between 9 and 7.

Code

Java

public class MaxDifference {
    public static int maxDifference(int[] arr) {
        int minVal = arr[0];
        int maxDiff = arr[1] - arr[0];
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] - minVal > maxDiff) {
                maxDiff = arr[i] - minVal;
            }
            if (arr[i] < minVal) {
                minVal = arr[i];
            }
        }
        return maxDiff;
    }

    public static void main(String[] args) {
        System.out.println(maxDifference(new int[]{2, 3, 10, 6, 4, 8, 1}));
    }
}

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

Question 5

Odd-Even Alternating Arrangement

Problem

Given an array of integers (equal number of odd and even values), arrange them so odd and even values alternate in non-decreasing order. If the smallest value is even, print Even-Odd pattern; if odd, print Odd-Even pattern.

Example:

Input: arr = [1, 3, 2, 5, 4, 7, 10]
Output: 1, 2, 3, 4, 5, 10, 7
Explanation: Smallest value is 1 (odd), so output follows Odd-Even pattern.

Input: arr = [9, 8, 13, 2, 19, 14]
Output: 2, 9, 8, 13, 14, 19
Explanation: Smallest value is 2 (even), so output follows Even-Odd pattern.

Code

Java

import java.util.*;
public class OddEvenAlternating {
    public static List<Integer> arrange(int[] arr) {
        List<Integer> odds = new ArrayList<>();
        List<Integer> evens = new ArrayList<>();
        for (int num : arr) {
            if (num % 2 == 0) evens.add(num);
            else odds.add(num);
        }
        Collections.sort(odds);
        Collections.sort(evens);

        List<Integer> result = new ArrayList<>();
        int minVal = Arrays.stream(arr).min().getAsInt();
        boolean startWithEven = (minVal % 2 == 0);

        int i = 0, j = 0;
        while (i < odds.size() || j < evens.size()) {
            if (startWithEven) {
                if (j < evens.size()) result.add(evens.get(j++));
                if (i < odds.size()) result.add(odds.get(i++));
            } else {
                if (i < odds.size()) result.add(odds.get(i++));
                if (j < evens.size()) result.add(evens.get(j++));
            }
        }
        return result;
    }

    public static void main(String[] args) {
        System.out.println(arrange(new int[]{1, 3, 2, 5, 4, 7, 10}));
    }
}

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

Question 6

Minimum Candies Distribution

Problem

Children sit in a line, each with a rating. Every child gets at least 1 candy. If two children sit next to each other, the one with the higher rating must get more candies. Minimize the total candies distributed.

Example:

Sample Input 0: ratings = [1, 2, 2]
Sample Output 0: 4
Explanation: Distribution [1, 2, 1] satisfies all constraints with minimum candies.

Sample Input 2: ratings = [2, 4, 3, 5, 2, 6, 4, 5, 2]
Sample Output 2: 12

Code

Java

public class Candies {
    public static int candies(int n, int[] arr) {
        int[] candyArr = new int[n];
        java.util.Arrays.fill(candyArr, 1);

        for (int i = 1; i < n; i++) {
            if (arr[i] > arr[i - 1]) candyArr[i] = candyArr[i - 1] + 1;
        }
        for (int i = n - 2; i >= 0; i--) {
            if (arr[i] > arr[i + 1]) candyArr[i] = Math.max(candyArr[i], candyArr[i + 1] + 1);
        }

        int total = 0;
        for (int c : candyArr) total += c;
        return total;
    }

    public static void main(String[] args) {
        System.out.println(candies(3, new int[]{1, 2, 2}));
    }
}

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

Question 7

Minimum Adjacent Swaps to Make a Palindrome

Problem

Given a string, find the minimum number of adjacent swaps required to make it a palindrome. If not possible, return -1.

Example:

Input: "aabcb"
Output: 3
Explanation: After 1st swap: abacb, After 2nd swap: abcab, After 3rd swap: abcba

Input: "adbcdbad"
Output: -1

Code

Java

public class MinSwapsToPalindrome {
    public static int minSwaps(String s) {
        char[] arr = s.toCharArray();
        int n = arr.length;
        int oddCount = 0;
        java.util.Map<Character, Integer> freq = new java.util.HashMap<>();
        for (char c : arr) freq.put(c, freq.getOrDefault(c, 0) + 1);
        for (int count : freq.values()) if (count % 2 != 0) oddCount++;
        if (oddCount > 1) return -1;

        int swaps = 0;
        int i = 0, j = n - 1;
        while (i < j) {
            if (arr[i] == arr[j]) {
                i++;
                j--;
            } else {
                int k = j;
                while (k > i && arr[k] != arr[i]) k--;
                if (k == i) {
                    char temp = arr[i];
                    arr[i] = arr[i + 1];
                    arr[i + 1] = temp;
                    swaps++;
                } else {
                    while (k < j) {
                        char temp = arr[k];
                        arr[k] = arr[k + 1];
                        arr[k + 1] = temp;
                        k++;
                        swaps++;
                    }
                    i++;
                    j--;
                }
            }
        }
        return swaps;
    }

    public static void main(String[] args) {
        System.out.println(minSwaps("aabcb"));
    }
}

Time: O(N²)Space: O(N)

Question 8

Remove All Occurrences of a Character

Problem

Given a string and a character x, remove all occurrences of x from the string.

Example:

Input: input1 = "Prepinsta", input2 = "i"
Output: "Prepnsta"
Explanation: All occurrences of 'i' are removed, keeping other characters.

Code

Java

public class RemoveCharacter {
    public static String removeChar(String s, char x) {
        StringBuilder result = new StringBuilder();
        for (char c : s.toCharArray()) {
            if (c != x) result.append(c);
        }
        return result.toString();
    }

    public static void main(String[] args) {
        System.out.println(removeChar("Prepinsta", 'i'));
    }
}

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

Question 9

Caesar Cipher Decryption (Shift by 3)

Problem

Encryption replaces each letter with the letter 3 positions to the left (e.g., 'a' → 'x', 'd' → 'a'). Given an encrypted string, find the corresponding plaintext.

Example:

Input: "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
Output: "XYZABCDEFGHIJKLMNOPQRSTUVW"

Input: "ATTACKATONCE"
Output: "EXXEGOEXSRGI"

Code

Java

public class CaesarCipherDecrypt {
    public static String decrypt(String ciphertext) {
        StringBuilder plaintext = new StringBuilder();
        for (char c : ciphertext.toCharArray()) {
            if (Character.isUpperCase(c)) {
                char decrypted = (char) ((c - 'A' + 3) % 26 + 'A');
                plaintext.append(decrypted);
            } else {
                plaintext.append(c);
            }
        }
        return plaintext.toString();
    }

    public static void main(String[] args) {
        System.out.println(decrypt("ATTACKATONCE"));
    }
}

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

public class VowelLCS { static boolean isVowel(char c) { return "aeiouAEIOU".indexOf(c) != -1; } public static int vowelLCS(String s1, String s2) { int m = s1.length(), n = s2.length(); int[][] dp = new int[m + 1][n + 1]; for (int i = 1; i <= m; i++) { for (int j = 1; j <= n; j++) { if (s1.charAt(i - 1) == s2.charAt(j - 1) && isVowel(s1.charAt(i - 1))) { dp[i][j] = dp[i - 1][j - 1] + 1; } else { dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]); } } } return dp[m][n]; } public static void main(String[] args) { System.out.println(vowelLCS("vowelpunish", "english")); } }

Input: n = 5, A = [5, 0, 3, 2, 9] Output: 3 Explanation: The longest decreasing subsequence is [5, 3, 2] Input: n = 9, A = [15, 27, 14, 38, 63, 55, 46, 65, 85] Output: 3 Explanation: The longest decreasing subsequence is [63, 55, 46]

public class LongestDecreasingSubsequence { public static int longestDecreasingSubsequence(int[] arr) { int n = arr.length; int[] dp = new int[n]; java.util.Arrays.fill(dp, 1); int maxLen = 1; for (int i = 1; i < n; i++) { for (int j = 0; j < i; j++) { if (arr[i] < arr[j]) { dp[i] = Math.max(dp[i], dp[j] + 1); } } maxLen = Math.max(maxLen, dp[i]); } return maxLen; } public static void main(String[] args) { System.out.println(longestDecreasingSubsequence(new int[]{5, 0, 3, 2, 9})); } }

public class MinPenalty { public static int minPenalty(int[] arr) { int penalty = 0; for (int i = 1; i < arr.length; i++) { penalty += Math.abs(arr[i] - arr[i - 1]); } return penalty; } public static void main(String[] args) { System.out.println(minPenalty(new int[]{5, 10, 1, 4, 8, 7})); } }

Input: arr = [2, 3, 10, 6, 4, 8, 1] Output: 8 Explanation: The maximum difference is between 10 and 2. Input: arr = [7, 9, 5, 6, 3, 2] Output: 2 Explanation: The maximum difference is between 9 and 7.

public class MaxDifference { public static int maxDifference(int[] arr) { int minVal = arr[0]; int maxDiff = arr[1] - arr[0]; for (int i = 1; i < arr.length; i++) { if (arr[i] - minVal > maxDiff) { maxDiff = arr[i] - minVal; } if (arr[i] < minVal) { minVal = arr[i]; } } return maxDiff; } public static void main(String[] args) { System.out.println(maxDifference(new int[]{2, 3, 10, 6, 4, 8, 1})); } }

Input: arr = [1, 3, 2, 5, 4, 7, 10] Output: 1, 2, 3, 4, 5, 10, 7 Explanation: Smallest value is 1 (odd), so output follows Odd-Even pattern. Input: arr = [9, 8, 13, 2, 19, 14] Output: 2, 9, 8, 13, 14, 19 Explanation: Smallest value is 2 (even), so output follows Even-Odd pattern.

import java.util.*; public class OddEvenAlternating { public static List<Integer> arrange(int[] arr) { List<Integer> odds = new ArrayList<>(); List<Integer> evens = new ArrayList<>(); for (int num : arr) { if (num % 2 == 0) evens.add(num); else odds.add(num); } Collections.sort(odds); Collections.sort(evens); List<Integer> result = new ArrayList<>(); int minVal = Arrays.stream(arr).min().getAsInt(); boolean startWithEven = (minVal % 2 == 0); int i = 0, j = 0; while (i < odds.size() || j < evens.size()) { if (startWithEven) { if (j < evens.size()) result.add(evens.get(j++)); if (i < odds.size()) result.add(odds.get(i++)); } else { if (i < odds.size()) result.add(odds.get(i++)); if (j < evens.size()) result.add(evens.get(j++)); } } return result; } public static void main(String[] args) { System.out.println(arrange(new int[]{1, 3, 2, 5, 4, 7, 10})); } }

Sample Input 0: ratings = [1, 2, 2] Sample Output 0: 4 Explanation: Distribution [1, 2, 1] satisfies all constraints with minimum candies. Sample Input 2: ratings = [2, 4, 3, 5, 2, 6, 4, 5, 2] Sample Output 2: 12

public class Candies { public static int candies(int n, int[] arr) { int[] candyArr = new int[n]; java.util.Arrays.fill(candyArr, 1); for (int i = 1; i < n; i++) { if (arr[i] > arr[i - 1]) candyArr[i] = candyArr[i - 1] + 1; } for (int i = n - 2; i >= 0; i--) { if (arr[i] > arr[i + 1]) candyArr[i] = Math.max(candyArr[i], candyArr[i + 1] + 1); } int total = 0; for (int c : candyArr) total += c; return total; } public static void main(String[] args) { System.out.println(candies(3, new int[]{1, 2, 2})); } }

public class MinSwapsToPalindrome { public static int minSwaps(String s) { char[] arr = s.toCharArray(); int n = arr.length; int oddCount = 0; java.util.Map<Character, Integer> freq = new java.util.HashMap<>(); for (char c : arr) freq.put(c, freq.getOrDefault(c, 0) + 1); for (int count : freq.values()) if (count % 2 != 0) oddCount++; if (oddCount > 1) return -1; int swaps = 0; int i = 0, j = n - 1; while (i < j) { if (arr[i] == arr[j]) { i++; j--; } else { int k = j; while (k > i && arr[k] != arr[i]) k--; if (k == i) { char temp = arr[i]; arr[i] = arr[i + 1]; arr[i + 1] = temp; swaps++; } else { while (k < j) { char temp = arr[k]; arr[k] = arr[k + 1]; arr[k + 1] = temp; k++; swaps++; } i++; j--; } } } return swaps; } public static void main(String[] args) { System.out.println(minSwaps("aabcb")); } }

public class RemoveCharacter { public static String removeChar(String s, char x) { StringBuilder result = new StringBuilder(); for (char c : s.toCharArray()) { if (c != x) result.append(c); } return result.toString(); } public static void main(String[] args) { System.out.println(removeChar("Prepinsta", 'i')); } }

public class CaesarCipherDecrypt { public static String decrypt(String ciphertext) { StringBuilder plaintext = new StringBuilder(); for (char c : ciphertext.toCharArray()) { if (Character.isUpperCase(c)) { char decrypted = (char) ((c - 'A' + 3) % 26 + 'A'); plaintext.append(decrypted); } else { plaintext.append(c); } } return plaintext.toString(); } public static void main(String[] args) { System.out.println(decrypt("ATTACKATONCE")); } }

LTIMindtree

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Practice Questions

Longest Common Subsequence of Vowels Only

Problem

Code

Longest Decreasing Subsequence

Problem

Code

Minimum Penalty (Sum of Absolute Differences)

Problem

Code

Maximum Difference with Larger Element Appearing After

Problem

Code

Odd-Even Alternating Arrangement

Problem

Code

Minimum Candies Distribution

Problem

Code

Minimum Adjacent Swaps to Make a Palindrome

Problem

Code

Remove All Occurrences of a Character

Problem

Code

Caesar Cipher Decryption (Shift by 3)

Problem

Code

LTIMindtree

Display Mode

Jump to Section

Other Content

Export

LTIMindtree coding

Practice Questions

Longest Common Subsequence of Vowels Only

Problem

Code

Longest Decreasing Subsequence

Problem

Code

Minimum Penalty (Sum of Absolute Differences)

Problem

Code

Maximum Difference with Larger Element Appearing After

Problem

Code

Odd-Even Alternating Arrangement

Problem

Code

Minimum Candies Distribution

Problem

Code

Minimum Adjacent Swaps to Make a Palindrome

Problem

Code

Remove All Occurrences of a Character

Problem

Code

Caesar Cipher Decryption (Shift by 3)

Problem

Code