LeetCode 560 Subarray Sum Equals K - Problem Statement

This is Subarray Sum Equals K from LeetCode. It's one of the most common prefix sum interview questions. Given an array of integers $nums$ and an integer $k$, return the total number of subarrays whose sum equals $k$.

At first, you might try checking every subarray. That's $O(n^2)$ subarrays, and even with prefix sums, you're still doing $O(n^2)$ comparisons. Can you do better?