Given an array of integers nums and an integer k, determine the total number of subarrays whose sum is exactly equal to k.

Note: A subarray is a contiguous, non empty sequence of elements within an array.

Constraints:

• $1 \leq$ nums.length $\leq 2 \times 10^4$

• $-1000 \leq$ nums[i] $\leq 1000$

• $-10^7 \leq$ ...