Single number and Single Number IIt

题目分别是：

Given an array of integers, every element appears twice except for one. Find that single one.

Given an array of integers, every element appears three times except for one. Find that single one.

开始考虑使用hashtable存储内容，查找，看了discuss发现使用异或这个方法

问题一的代码如下：

public class Solution {
    public int singleNumber(int[] A) {
    int i = 0;
    int result = 0;
    for (i=0; i<=A.length-1; i++){
        result = result ^ A[i];
        
    }

    return result;
        
    }
}

问题二看了discuss 发现神解答如下：

http://oj.leetcode.com/discuss/857/constant-space-solution