Find the Missing Number Show result

Given an array contains N numbers of 0 .. N, find which number doesn't exist in the array.

Have you met this question in a real interview? 

Yes

Example

Given N = 3 and the array [0, 1, 3], return 2.

Challenge

Do it in-place with O(1) extra memory and O(n) time.

public class Solution {
    /**  
     * @param nums: an array of integers
     * @return: an integer
     */
    public int findMissing(int[] nums) {
        // write your code here
        int n = nums.length;
        int sum = (n+1) * n / 2;
        for(int num : nums){
            sum -= num;
        }
        return sum;
    }
}

public class Solution {
    /**  
     * @param nums: an array of integers
     * @return: an integer
     */
    public int findMissing(int[] nums) {
        // write your code here
        int xor = 0;
        for(int i = 0; i <= nums.length; i++){
            xor ^= i;
        }
       
         for(int num : nums){
            xor ^= num;
        }
       
       
        return xor;
    }
}