# Find maximum (or minimum) sum of a subarray of size k in C++

In this problem, we are given an  array arr[] and a number k. Our task is to Find the maximum (or minimum) sum of a subarray of size k.

Let’s take an example to understand the problem,

Input: arr[] = {55, 43, 12, 76, 89, 25, 99} , k = 2

Output: 165

Explanation:

The subarray of size 2 has sum = 76 + 89 = 165

## Solution Approach

A simple approach to solve the problem is by finding all k sized subarrays and then return the sum with maximum value.

Another Approach is using the sliding window, we will find the sum of k sized subarrayes. For this, the next k sized subarray, we will subtract the last index element and add the next index element.

And then return the subarray sum with the maximum value.

## Example

Live Demo

#include <iostream>
using namespace std;

int findMaxSumSubarray(int arr[], int n, int k) {

if (n < k) {
cout << "Invalid";
return -1;
}

int maxSum = 0;
for (int i=0; i<k; i++)
maxSum += arr[i];
int curr_sum = maxSum;
for (int i=k; i<n; i++) {
curr_sum += arr[i] - arr[i-k];
maxSum = max(maxSum, curr_sum);
}
return maxSum;
}

int main() {

int arr[] = {55, 43, 12, 76, 89, 25, 99};
int n = sizeof(arr)/sizeof(arr);
int k = 2;
cout<<"The sum of subarray with max sum of size "<<k<<" is "<<findMaxSumSubarray(arr, n, k);
return 0;
}

## Output

The sum of subarray with max sum of size 2 is 165