Window Sliding Technique is a useful way to solve some problem here is a live example of it

https://www.geeksforgeeks.org/window-sliding-technique/

 working example

https://www.onlinegdb.com/edit/BJX3JA0Zv

code =>

#include <stdio.h>

#include<iostream>

#include<vector>

using namespace std;

//https://www.geeksforgeeks.org/window-sliding-technique/

int Windowslidingtechnique(vector<int> &vec,int element)

{

     //get sum

     int sum=0;

     for(int i=0;i<element;i++)

     {

         sum+=vec.at(i);

     }

     //sliding window technique

     int windowSum=sum;

     int maxSum=0;

     for(int i=element;i<vec.size();i++)

     {

         windowSum+=vec.at(i)-vec.at(i-element);

         maxSum=max(maxSum,windowSum);

     }

     return maxSum;

}

int main()

{

    vector<int> vec={ 1, 4, 2, 10, 2, 3, 1, 0, 20 }; 

    int k = 4; 

    std::cout << Windowslidingtechnique(vec,k) << std::endl;

    return 0;

}