leetcode-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?

在数组中，数字皆成对出现，找出唯一一个单独的数字。

思路：a^a=0,相同数字异或为0.

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