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: 28

Explanation: The maximum result is 5 ^ 25 = 28.

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