Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k.
A subarray is a contiguous non-empty sequence of elements within an array.
1 <= nums.length <= 2 * 10^4-1000 <= nums[i] <= 1000-10^7 <= k <= 10^7nums = [1,1,1], k = 22nums = [1,2,3], k = 32