Maximum XOR of Two Numbers
mediumTime: O(n)Space: O(n)
Recognize the pattern
maximize XOR of two numbersbinary triegreedy bit choice
Brute force idea
XOR every pair — O(n²).
Better approach
Binary trie (MSB to LSB). For each number, walk trie choosing opposite bit at each level. O(32n).
Key invariant
Opposite bits maximize XOR. Trie enables greedy bit-by-bit maximization in O(32) per number.
Watch out for
Using decimal trie — it's a BINARY trie with 2 children per node.