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 index = 1;
        for(; index < A.length; ++index){
            A[index] = A[index]^A[index-1];
        }
        return A[index - 1];
    }
}