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# 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.
```

```java
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;
    }
}
```