Leetcode 1803. Count Pairs With XOR in a Range

Count the number of index pairs (i<j) whose XOR falls within [low, high]; the challenge is to do better than O(n^2) by computing, for each element, how many previous elements produce XOR ≤ bound and using a binary trie (bitwise prefix tree) to get an O(n log C) solution (C = max value range).