560. Subarray Sum Equals K

class Solution:
    def subarraySum(self, A: List[int], k: int) -> int:
        d = defaultdict(int, {0: 1})
        prefix = 0
        count = 0

        for v in A:
            prefix = prefix + v
            count = count + d[prefix - k]
            d[prefix] = d[prefix] + 1
        
        return count