K-Element Sum Ranges

You are given an array of integers and a value K. Your task is to find the total count of unique subarrays whose sum equals K. You must implement an efficient solution using prefix sums to avoid recalculating sums. Input: - The first line contains integers n (1 ≤ n ≤ 100,000) and K (1 ≤ K ≤ 1,000,000). - The second line contains n integers a[i] (−10000 ≤ a[i] ≤ 10000) representing the elements of the array. Output: - Output a single integer, the count of unique subarrays that sum up to K. Example: Input: 5 5 1 2 3 -2 4 Output: 2