Linked Url:https://leetcode.com/problems/single-number/

Given a non-empty 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?

Example 1:

Input: [2,2,1]
Output: 1

Example 2:

Input: [4,1,2,1,2]
Output: 4

solution:

The method is xor option, principles is  : 0 xor 0 = 0; 0 xor 1 = 1；any  num xor itself  =  0,so we pass the array and xor its elements all,so the result  which is we want.

Ac code follow: 

1 class Solution {
2 public:
3     int singleNumber(vector<int>& nums) {
4         int res = nums[0];
5         for(int i = 1;i < nums.size();++i)
6             res = nums[i]^res;
7         return res;
8     }
9 };