Subarray sum equals K

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

        from collections import defaultdict
        prefixSumCounter = defaultdict(int)

        running_sum = 0
        count = 0

        for num in nums:
            running_sum += num

            # This would be so wrong because if k = 0, you would be double counting
            # prefixSumCounter[running_sum] += 1

            if running_sum == k:
                count += 1

            if running_sum - k in prefixSumCounter:

                # prefix_sum[running_sum - k] gives the number of times the sum running_sum - k has occurred
                # before reaching the current index j.So what we are trying to find how many such j's such that
                # prefixSums has value = running_sum - k
                # by this you are counting all subarry ending at this index but but but you want to exclude
                # counting of prefix sums in it because that is something you are already doing.
                count += prefixSumCounter[running_sum - k]

            #  You ensure that only previously encountered prefixSums are considered when checking for (running_sum - k)
            prefixSumCounter[running_sum] += 1

        return count