421. Maximum XOR of Two Numbers in an Array

Problem

Given an integer array nums, return **the maximum result of **nums[i] XOR nums[j], where 0 <= i <= j < n.

  Example 1:

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

Example 2:

Input: nums = [14,70,53,83,49,91,36,80,92,51,66,70]
Output: 127

  Constraints:

• 1 <= nums.length <= 2 * 10^5

• 0 <= nums[i] <= 2^31 - 1

Solution (Java)

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

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).