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