【LeetCode】 421. Maximum XOR of Two Numbers in an Array

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.

public class Solution {    public int findMaximumXOR(int[] nums) {        int max = 0, mask = 0;        for(int i = 31; i >= 0; i--){            mask = mask | (1 << i);            Set<Integer> set = new HashSet<>();            for(int num : nums){                set.add(num & mask);            }            int tmp = max | (1 << i);            for(int prefix : set){                if(set.contains(tmp ^ prefix)) {                    max = tmp;                    break;                }            }        }        return max;    }}