leetcode 136. Single Number && 137. Single Number II

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?

异或运算应用：

　　异或运算满足交换律和结合律, 通过交换元素(如插入排序等)可以使得相同元素相邻，

(x, x), (y, y), ..., sigle, ... , (z, z)

所有元素异或后：(x ^ x) ^ ... ^ single ^ (z ^ z) = 0 ^ ... ^ single ^ ... ^ 0 = single

1 int singleNumber(int A[], int n)
2     {
3         int single = 0;
4
5         for (int i = 0; i < n; i++)
6             single ^= A[i];
7
8         return single;
9     }