Given a non-empty array of numbers, a0, a1, a2, … , an-1, where 0 ≤ ai < 231.Find the maximum result of ai XOR aj, where 0 ≤ i, j < n.Could you do this in O(n) runtime?Example:Input: [3, 10, 5, 25, 2, 8]Output: 28Explanation: The maximum result is 5 ^ 25 = 28.

Solution 1: Bit Manipulation:

这题真心有点难，get the max XOR bit by bit

note that if A^B=C, then A^C=B, B^C=A

1 public class Solution { 2     public int findMaximumXOR(int[] nums) { 3         int mask = 0, max = 0; 4         for (int i=31; i>=0; i--) { 5             mask |= 1<
     
       prefixes = new HashSet
      
       (); 7             for (int each : nums) { 8                 prefixes.add(each & mask); // reserve Left bits and ignore Right bits 9             }10             int tmpMax = max | (1<
      
     

Solution 2: Trie, (未研究)

https://discuss.leetcode.com/topic/63207/java-o-n-solution-using-trie

https://discuss.leetcode.com/topic/64753/31ms-o-n-java-solution-using-trie