Variable_size_window.java

public static void main(String[] args) {
        FastReader s = new FastReader();
        int n = s.nextInt();
        int k = s.nextInt();
        int a[] = new int[n];
        for (int i = 0; i < n; i++)
            a[i] = s.nextInt();

        int left=0, right=0, sum=0;
        int max = Integer.MIN_VALUE;
        while(right < n){
            sum += a[right]; //summing of the right end of window

            if(sum < k)
                right++; // if sum < k increase the right end of window pane
            
            else if(sum == k){
                max = Math.max(max, right-left+1); // If the condition is reached update max with the size of window
                right++;
            }
            
            else if(sum > k){ //If sum > k subtract the left side of the pane and maintain the sum == k
                while(sum > k){
                    sum -= a[left];
                    left++;
                }
                right++;
            }
        }
        System.out.println(max);
    }