Java Program to Find the K-th Largest Sum Contiguous Subarray

// Java program to find the k-th 
// largest sum of subarray
import java.util.*;

class KthLargestSumSubArray
{
    // function to calculate kth largest 
    // element in contiguous subarray sum
    static int kthLargestSum(int arr[], int n, int k)
    {
        // array to store prefix sums
        int sum[] = new int[n + 1];
        sum[0] = 0;
        sum[1] = arr[0];
        for (int i = 2; i <= n; i++)
            sum[i] = sum[i - 1] + arr[i - 1];
        
        // priority_queue of min heap
        PriorityQueue<Integer> Q = new PriorityQueue<Integer> ();
        
        // loop to calculate the contiguous subarray
        // sum position-wise
        for (int i = 1; i <= n; i++)
        {
    
            // loop to traverse all positions that
            // form contiguous subarray
            for (int j = i; j <= n; j++)
            {
                // calculates the contiguous subarray
                // sum from j to i index
                int x = sum[j] - sum[i - 1];
    
                // if queue has less then k elements,
                // then simply push it
                if (Q.size() < k)
                    Q.add(x);
    
                else
                {
                    // if the min heap has equal to
                    // k elements then just check
                    // if the largest kth element is
                    // smaller than x then insert
                    // else it's of no use
                    if (Q.peek() < x)
                    {
                        Q.poll();
                        Q.add(x);
                    }
                }
            }
        }
        
        // the top element will be the kth
        // largest element
        return Q.poll();
    }
    
    // Driver Code
    public static void main(String[] args) 
    {
        int a[] = new int[]{ 10, -10, 20, -40 };
        int n = a.length;
        int k = 6;

        // calls the function to find out the
        // k-th largest sum
        System.out.println(kthLargestSum(a, n, k)); 
    }
}

/* This code is contributed by Danish Kaleem */