Leetcode 3224. Minimum Array Changes to Make Differences Equal

Given an even-length array and allowed values 0..k, find the minimum number of element replacements so that every mirrored pair satisfies |a[i] - a[n-1-i]| = X for the same X. The core challenge is to aggregate per-pair costs (0/1/2 changes) across all candidate X efficiently and pick the X that minimizes the total changes.