Minimum number of swaps required such that a given substring consists of exactly K 1s

// Java program for the above approach

import java.io.*;
import java.util.*;

class GFG {

    // Function to find the minimum number
    // of swaps required such that the
    // substring {s[l], .., s[r]} consists
    // of exactly k 1s
    static int minimumSwaps(
        String s, int l, int r, int k)
    {
        // Store the size of the string
        int n = s.length();

        // Store the total number of 1s
        // and 0s in the entire string
        int tot_ones = 0, tot_zeros = 0;

        // Traverse the string S to find
        // the frequency of 1 and 0
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '1')
                tot_ones++;
            else
                tot_zeros++;
        }

        // Store the number of 1s and
        // 0s in the substring s[l, r]
        int ones = 0, zeros = 0, sum = 0;

        // Traverse the substring S[l, r]
        // to find the frequency of 1s
        // and 0s in it
        for (int i = l - 1; i < r; i++) {
            if (s.charAt(i) == '1') {
                ones++;
                sum++;
            }
            else
                zeros++;
        }

        // Store the count of 1s and
        // 0s outside substring s[l, r]
        int rem_ones = tot_ones - ones;
        int rem_zeros = tot_zeros - zeros;

        // Check if the sum of the
        // substring is at most K
        if (k >= sum) {

            // Store number of 1s required
            int rem = k - sum;

            // Check if there are enough 1s
            // remaining to be swapped
            if (zeros >= rem && rem_ones >= rem)
                return rem;
        }

        // If the count of 1s in the substring exceeds k
        else if (k < sum) {

            // Store the number of 0s required
            int rem = sum - k;

            // Check if there are enough 0s
            // remaining to be swapped
            if (ones >= rem && rem_zeros >= rem)
                return rem;
        }

        // In all other cases, print -1
        return -1;
    }

    // Driver Code
    public static void main(String[] args)
    {
        String S = "110011111000101";
        int L = 5, R = 8, K = 2;
        System.out.println(
            minimumSwaps(S, L, R, K));
    }
}