# K-th Largest Sum Contiguous Subarray

• Difficulty Level : Medium
• Last Updated : 22 Aug, 2022

Given an array of integers. Write a program to find the K-th largest sum of contiguous subarray within the array of numbers that has both negative and positive numbers.

Examples:

Input: a[] = {20, -5, -1}, K = 3
Output: 14
Explanation: All sum of contiguous subarrays are (20, 15, 14, -5, -6, -1)
so the 3rd largest sum is 14.

Input: a[] = {10, -10, 20, -40}, k = 6
Output: -10
Explanation: The 6th largest sum among
sum of all contiguous subarrays is -10.

Brute force Approach: Store all the contiguous sums in another array and sort it and print the Kth largest. But in the case of the number of elements being large, the array in which we store the contiguous sums will run out of memory as the number of contiguous subarrays will be large (quadratic order)

## Kth largest sum contiguous subarray using Min-Heap:

The key idea is to store the pre-sum of the array in a sum[] array. One can find the sum of contiguous subarray from index i to j as sum[j] – sum[i-1]. Now generate all possible contiguous subarray sums and push them into the Min-Heap only if the size of Min-Heap is less than K or the current sum is greater than the root of the Min-Heap. In the end, the root of the Min-Heap is the required answer

Follow the given steps to solve the problem using the above approach:

• Create a prefix sum array of the input array
• Create a Min-Heap that stores the subarray sum
• Iterate over the given array using the variable i such that 1 <= i <= N, here i denotes the starting point of the subarray
• Create a nested loop inside this loop using a variable j such that i <= j <= N, here j denotes the ending point of the subarray
• Calculate the sum of the current subarray represented by i and j, using the prefix sum array
• If the size of the Min-Heap is less than K, then push this sum into the heap
• Otherwise, if the current sum is greater than the root of the Min-Heap, then pop out the root and push the current sum into the Min-Heap
• Now the root of the Min-Heap denotes the Kth largest sum, Return it

Below is the implementation of the above approach:

## C++

 `// C++ program to find the K-th largest sum` `// of subarray` `#include ` `using` `namespace` `std;`   `// Function to calculate Kth largest element` `// in contiguous subarray sum` `int` `kthLargestSum(``int` `arr[], ``int` `N, ``int` `K)` `{` `    ``// array to store prefix sums` `    ``int` `sum[N + 1];` `    ``sum = 0;` `    ``sum = arr;` `    ``for` `(``int` `i = 2; i <= N; i++)` `        ``sum[i] = sum[i - 1] + arr[i - 1];`   `    ``// priority_queue of min heap` `    ``priority_queue<``int``, vector<``int``>, greater<``int``> > Q;`   `    ``// 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.push(x);`   `            ``else` `{` `                ``// it the min heap has equal to` `                ``// k elements then just check` `                ``// if the largest kth element is` `                ``// smaller than x then insert` `                ``// else its of no use` `                ``if` `(Q.top() < x) {` `                    ``Q.pop();` `                    ``Q.push(x);` `                ``}` `            ``}` `        ``}` `    ``}`   `    ``// the top element will be then kth` `    ``// largest element` `    ``return` `Q.top();` `}`   `// Driver's code` `int` `main()` `{` `    ``int` `a[] = { 10, -10, 20, -40 };` `    ``int` `N = ``sizeof``(a) / ``sizeof``(a);` `    ``int` `K = 6;`   `    ``// Function call` `    ``cout << kthLargestSum(a, N, K);` `    ``return` `0;` `}`

## Java

 `// 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 Q` `            ``= ``new` `PriorityQueue();`   `        ``// 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` `{` `                    ``// it the min heap has equal to` `                    ``// k elements then just check` `                    ``// if the largest kth element is` `                    ``// smaller than x then insert` `                    ``// else its of no use` `                    ``if` `(Q.peek() < x) {` `                        ``Q.poll();` `                        ``Q.add(x);` `                    ``}` `                ``}` `            ``}` `        ``}`   `        ``// the top element will be then kth` `        ``// largest element` `        ``return` `Q.poll();` `    ``}`   `    ``// Driver's Code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``int` `a[] = ``new` `int``[] { ``10``, -``10``, ``20``, -``40` `};` `        ``int` `N = a.length;` `        ``int` `K = ``6``;`   `        ``// Function call` `        ``System.out.println(kthLargestSum(a, N, K));` `    ``}` `}`   `/* This code is contributed by Danish Kaleem */`

## Python3

 `# Python program to find the K-th largest sum` `# of subarray` `import` `heapq`   `# function to calculate Kth largest element` `# in contiguous subarray sum`     `def` `kthLargestSum(arr, N, K):`   `    ``# array to store prefix sums` `    ``sum` `=` `[]` `    ``sum``.append(``0``)` `    ``sum``.append(arr[``0``])` `    ``for` `i ``in` `range``(``2``, N ``+` `1``):` `        ``sum``.append(``sum``[i ``-` `1``] ``+` `arr[i ``-` `1``])`   `    ``# priority_queue of min heap` `    ``Q ``=` `[]` `    ``heapq.heapify(Q)`   `    ``# loop to calculate the contiguous subarray` `    ``# sum position-wise` `    ``for` `i ``in` `range``(``1``, N ``+` `1``):`   `        ``# loop to traverse all positions that` `        ``# form contiguous subarray` `        ``for` `j ``in` `range``(i, N ``+` `1``):` `            ``x ``=` `sum``[j] ``-` `sum``[i ``-` `1``]`   `            ``# if queue has less then k elements,` `            ``# then simply push it` `            ``if` `len``(Q) < K:` `                ``heapq.heappush(Q, x)` `            ``else``:` `                ``# it the min heap has equal to` `                ``# k elements then just check` `                ``# if the largest kth element is` `                ``# smaller than x then insert` `                ``# else its of no use` `                ``if` `Q[``0``] < x:` `                    ``heapq.heappop(Q)` `                    ``heapq.heappush(Q, x)`   `    ``# the top element will be then kth` `    ``# largest element` `    ``return` `Q[``0``]`     `# Driver's code` `if` `__name__ ``=``=` `"__main__"``:` `    ``a ``=` `[``10``, ``-``10``, ``20``, ``-``40``]` `    ``N ``=` `len``(a)` `    ``K ``=` `6`   `    ``# Function call` `    ``print``(kthLargestSum(a, N, K))`     `# This code is contributed by Kumar Suman`

## C#

 `// C# program to find the K-th` `// largest sum of subarray`   `using` `System;` `using` `System.Collections.Generic;` `public` `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;` `        ``sum = arr;` `        ``for` `(``int` `i = 2; i <= N; i++)` `            ``sum[i] = sum[i - 1] + arr[i - 1];`   `        ``// priority_queue of min heap` `        ``List<``int``> Q = ``new` `List<``int``>();`   `        ``// 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.Count < K)` `                    ``Q.Add(x);`   `                ``else` `{` `                    ``// it the min heap has equal to` `                    ``// k elements then just check` `                    ``// if the largest kth element is` `                    ``// smaller than x then insert` `                    ``// else its of no use` `                    ``Q.Sort();` `                    ``if` `(Q < x) {` `                        ``Q.RemoveAt(0);` `                        ``Q.Add(x);` `                    ``}` `                ``}` `                ``Q.Sort();` `            ``}` `        ``}`   `        ``// the top element will be then Kth` `        ``// largest element` `        ``return` `Q;` `    ``}`   `    ``// Driver's Code` `    ``public` `static` `void` `Main(String[] args)` `    ``{` `        ``int``[] a = ``new` `int``[] { 10, -10, 20, -40 };` `        ``int` `N = a.Length;` `        ``int` `K = 6;`   `        ``// Function call` `        ``Console.WriteLine(kthLargestSum(a, N, K));` `    ``}` `}`   `// This code contributed by Rajput-Ji`

## JavaScript

 `// Javascript program to find the k-th largest sum` `// of subarray`   `// function to calculate kth largest element` `// in contiguous subarray sum` `function` `kthLargestSum(arr, n, k)` `{` `    ``// array to store prefix sums` `    ``var` `sum = ``new` `Array(n + 1);` `    ``sum = 0;` `    ``sum = arr;` `    ``for` `(``var` `i = 2; i <= n; i++)` `        ``sum[i] = sum[i - 1] + arr[i - 1];`   `    ``// priority_queue of min heap` `    ``var` `Q = [];`   `    ``// loop to calculate the contiguous subarray` `    ``// sum position-wise` `    ``for` `(``var` `i = 1; i <= n; i++)` `    ``{`   `        ``// loop to traverse all positions that` `        ``// form contiguous subarray` `        ``for` `(``var` `j = i; j <= n; j++)` `        ``{` `            ``// calculates the contiguous subarray` `            ``// sum from j to i index` `            ``var` `x = sum[j] - sum[i - 1];`   `            ``// if queue has less then k elements,` `            ``// then simply push it` `            ``if` `(Q.length < k)` `                ``Q.push(x);`   `            ``else` `            ``{` `                ``// it the min heap has equal to` `                ``// k elements then just check` `                ``// if the largest kth element is` `                ``// smaller than x then insert` `                ``// else its of no use` `                ``Q.sort();` `                ``if` `(Q < x)` `                ``{` `                    ``Q.pop();` `                    ``Q.push(x);` `                ``}` `            ``}` `            `  `            ``Q.sort();` `        ``}` `    ``}`   `    ``// the top element will be then kth` `    ``// largest element` `    ``return` `Q;` `}`   `// Driver program to test above function` `var` `a = [ 10, -10, 20, -40 ];` `var` `n = a.length;` `var` `k = 6;`   `// calls the function to find out the` `// k-th largest sum` `document.write(kthLargestSum(a, n, k));`

Output

`-10`

Time Complexity: O(N2 log K)
Auxiliary Space: O(N), but this can be reduced to O(K) for min-heap and we can store the prefix sum array in the input array itself as it is of no use.

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