LeetCode 1879 Minimum XOR Sum of Two Arrays - Problem Statement

Given two arrays nums1 and nums2 of length $n$, rearrange nums2 to find the smallest XOR sum: $\sum_{i=0}^{n-1} (\text{nums1}[i] \oplus \text{nums2}[p[i]])$ where $p$ is a permutation. Example: nums1 $= [1, 2]$, nums2 $= [2, 3]$. If we pair $1$ with $3$ and $2$ with $2$: $(1 \oplus 3) + (2 \oplus 2) = 2 + 0 = 2$.

This is minimum. This is the assignment problem: match each element of nums1 to a unique element of nums2. The bitmask tracks which elements of nums2 have been used.