Single Number

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

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

public class Solution {
　　public int singleNumber(int[] A) {
　　　　int a = 0;
　　　　for(int i = 0; i < A.length; i++){
　　　　　　a ^= A[i];
　　　　}
　　　　return a;
　　}
}