find a max sum of subarray of size k{3 here}.

Example :

1) arr[] : {3,2,4,5,2,1,1,1,1,3,3} , sum = 5, k = 2:

output : [4,5] = 9

class Sliding{
    int findMax(int arr[], int k, int size){
        int i = 0; 
        int j = 0;
        int sum = 0;
        int max = 0;
        while(j < size){
            sum = sum + arr[j];
            if(j - i + 1 < k)
                j++;
            else if(j - i + 1 == k){
                sum -= arr[i];
                i++;
                j++;
            }
        }
        return sum;
    }
}