[子数组]和为k的子数组（前缀和）

class Solution:
    def subarraySum(self, nums: List[int], k: int) -> int:
        map = {0: 1}
        cur_sum = 0
        counter = 0
        for i in nums:
            cur_sum += i
            counter += map.get(cur_sum - k, 0)
            map[cur_sum] = map.get(cur_sum, 0) + 1

        return counter