268. Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array.

For example,
Given nums = [0, 1, 3] return 2.

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

public class Solution {
    public int missingNumber(int[] nums) {
        if (nums == null || nums.length == 0) return 0;
        int res = nums.length;

        for (int i = 0; i < nums.length; i++) res ^= (i ^ nums[i]);

        return res;
    }
}