Leetcode 3513. Number of Unique XOR Triplets I

Given a permutation of 1..n, count how many distinct values can be formed as nums[i] XOR nums[j] XOR nums[k] with i <= j <= k (so repeats allowed). With n up to 1e5, the challenge is to compute the size of this set efficiently by exploiting bitwise/XOR properties and combinatorial structure rather than brute force.