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 result = A[0];
        for (int i = 1; i < A.length; i++)
            result = result ^ A[i];
        return result;
    }
}