Get the Maximum XOR of Two Numbers in an Array in Java

The challenge

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 ≤ ij < n.

Could you do this in O(n) runtime?


Input: [3, 10, 5, 25, 2, 8]
Output: 28
Explanation: The maximum result is 5 ^ 25 = 28.

The solution in Java

We can very quickly resolve this challenge by performing a double loop and comparing our resultant:

class Solution {
    public int findMaximumXOR(int[] nums) {
        // store our maximum
        int max = 0;
        // loop through all numbers
        for (int i=0; i<nums.length; i++) {
            // loop through all our numbers again
            for (int j=0; j<nums.length; j++) {
                // keep a temp of the XOR
                int tmp = nums[i] ^ nums[j];
                // check if it's bigger
                if (tmp>max) max = tmp;

        // return our maximum        
        return max;

While this solution does come to a correct answer, it is not in the O(n) of time due to our second loop, and our space complexity could be made better by not using an additional variable.

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