Leetcode Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Could you implement it without using extra memory?

    public int singleNumber(int[] A) {        // Note: The Solution object is instantiated only once and is reused by each test case.        int res = 0;          for(int i =0;i<A.length;i++)              res ^= A[i];          return res;     }