class Solution:
    def subarraySum(self, nums: List[int], k: int) -> int:

        from collections import defaultdict
        prefix_sum = defaultdict(int)
        running_sum = 0
        count = 0

        for num in nums:
            running_sum = running_sum + num

            if running_sum == k:
                count = count + 1

            if running_sum - k in prefix_sum:
                count = count + prefix_sum[running_sum - k]

            prefix_sum[running_sum] += 1

        return count