Find the XOR of Numbers Which Appear Twice

You are given an array nums, where each number in the array appears either once or twice.

Return the bitwise XOR of all the numbers that appear twice in the array, or 0 if no number appears twice.

LeetCode Problem - 3158

import java.util.HashMap;
import java.util.Map;

class Solution {
    public int duplicateNumbersXOR(int[] nums) {
        // Create a HashMap to store the frequency of each number in the array
        Map<Integer, Integer> map = new HashMap<>();

        // Iterate over each number in the array
        for (int num : nums) {
            // Increment the count of the number in the map
            map.put(num, map.getOrDefault(num, 0) + 1);
        }

        // Initialize a variable to hold the XOR of duplicate numbers
        int xor = 0;

        // Iterate over the keys in the map (unique numbers in the array)
        for (int num : map.keySet()) {
            // Get the frequency of the current number
            int value = map.get(num);

            // If the number appears exactly twice, XOR it with the current xor value
            if (value == 2) xor ^= num;
        }

        // Return the final XOR result
        return xor;
    }
}