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##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
The approach
Track prefix sums in a hash map. Count occurrences of prefixSum - k.
function subarraySum(nums, k): count = 0 prefixSum = 0 sumCount = {0: 1} for num in nums: prefixSum += num if prefixSum - k in sumCount: count += sumCount[prefixSum - k] sumCount[prefixSum] = sumCount.get(prefixSum, 0) + 1 return count
time, space.
