Binary Subarrays With Sum.cpp

class Solution

{
public:
    int numSubarraysWithSum(vector<int> &A, int K)
    {
        return (countAtLeastK(A, K) - countAtLeastK(A, K + 1));
    }
    int countAtLeastK(vector<int> &A, int K)
    {
        int size = A.size();
        int answer = 0;
        int windowSum = 0;
        for (int left = 0, right = 0; right < size; right++)
        {
            windowSum += A[right];
            while (left <= right && windowSum >= K)
            {
                windowSum -= A[left];
                left++;
            }
            answer += left;
        }
        return answer;
    }
};