Tech Mahindra coding

public class DecimalToBinary {
    public static String decimalToBinary(int num) {
        if (num == 0) return "0";
        StringBuilder binary = new StringBuilder();
        while (num > 0) {
            binary.insert(0, num % 2);
            num /= 2;
        }
        return binary.toString();
    }

    public static void main(String[] args) {
        System.out.println(decimalToBinary(10));
    }
}

def decimal_to_binary(num):
    if num == 0:
        return "0"
    binary = ""
    while num > 0:
        binary = str(num % 2) + binary
        num //= 2
    return binary

print(decimal_to_binary(10))

public class LongestPalindromicSubstring {
    public static String longestPalindrome(String s) {
        if (s == null || s.length() < 1) return "";
        int start = 0, end = 0;
        for (int i = 0; i < s.length(); i++) {
            int len1 = expandFromCenter(s, i, i);
            int len2 = expandFromCenter(s, i, i + 1);
            int len = Math.max(len1, len2);
            if (len > end - start) {
                start = i - (len - 1) / 2;
                end = i + len / 2;
            }
        }
        return s.substring(start, end + 1);
    }

    private static int expandFromCenter(String s, int left, int right) {
        while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
            left--;
            right++;
        }
        return right - left - 1;
    }

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

def longest_palindrome(s):
    if not s:
        return ""

    def expand_from_center(left, right):
        while left >= 0 and right < len(s) and s[left] == s[right]:
            left -= 1
            right += 1
        return s[left + 1:right]

    result = ""
    for i in range(len(s)):
        odd = expand_from_center(i, i)
        even = expand_from_center(i, i + 1)
        result = max(result, odd, even, key=len)
    return result

print(longest_palindrome("babad"))

public class TotalProductsPerClient {
    public static int[] totalProducts(int[] orderIDs) {
        int[] result = new int[orderIDs.length];
        for (int i = 0; i < orderIDs.length; i++) {
            int orderID = orderIDs[i];
            int sum = 0;
            while (orderID > 0) {
                sum += orderID % 10;
                orderID /= 10;
            }
            result[i] = sum;
        }
        return result;
    }

    public static void main(String[] args) {
        int[] result = totalProducts(new int[]{23, 15, 7});
        for (int r : result) System.out.print(r + " ");
    }
}

public class NuclearEnergyProduction {
    public static long totalEnergy(long A, long R, int N) {
        long total = 0;
        long current = A;
        for (int i = 0; i < N; i++) {
            total += current;
            current *= R;
        }
        return total;
    }

    public static void main(String[] args) {
        System.out.println(totalEnergy(2, 3, 4));
    }
}

import java.util.*;
public class MaxPyramidHeight {
    public static int maxHeight(int[] widths) {
        Arrays.sort(widths);
        int height = 0;
        long prevLevelWidth = Long.MAX_VALUE;
        long currentLevelWidth = 0;
        int i = widths.length - 1;

        while (i >= 0) {
            currentLevelWidth = 0;
            int count = 0;
            while (i >= 0 && currentLevelWidth + widths[i] < prevLevelWidth) {
                currentLevelWidth += widths[i];
                count++;
                i--;
            }
            if (count == 0) break;
            height++;
            prevLevelWidth = currentLevelWidth;
        }
        return height;
    }
}

public class KthPositionAfterSwaps {
    public static int kthPositionAfterSwaps(int n, int[][] swaps, int k) {
        int[] arr = new int[n + 1];
        for (int i = 1; i <= n; i++) arr[i] = i;

        for (int[] swap : swaps) {
            int temp = arr[swap[0]];
            arr[swap[0]] = arr[swap[1]];
            arr[swap[1]] = temp;
        }
        return arr[k];
    }

    public static void main(String[] args) {
        int[][] swaps = {{1, 2}, {3, 4}};
        System.out.println(kthPositionAfterSwaps(5, swaps, 2));
    }
}