Subarray Sum Equals K

Given an integer array nums and an integer k, return the number of subarrays whose sum equals k.

Function signature

func SubarraySumK(nums []int, k int) int

Example

nums = [1,2,3,-2,5]
k = 3
output = 4

Constraints

• 0 <= len(nums) <= 200000
• -1_000_000_000 <= nums[i] <= 1_000_000_000
• -1_000_000_000 <= k <= 1_000_000_000

Notes

• Use a prefix-sum map to count occurrences.