LeetCode-in-Java

421. Maximum XOR of Two Numbers in an Array

Medium

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 * 105
• 0 <= nums[i] <= 231 - 1

Solution

import java.util.HashSet;
import java.util.Set;

public 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;
    }
}

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