Leetcoder - 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) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int ret = 0;
        for (int k : A) {
            ret ^= k;
        }
        return ret;
    }
}