136. Single Number

      史上最水的题。。。当然如果用了sort...

      

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?

class Solution {public:    int singleNumber(vector<int>& nums) {        if(nums.size()==1)return nums[0];    sort(nums.begin(),nums.end());   for(int i=0;i<nums.size()-1;i+=2)  {if(nums[i]!=nums[i+1])   return nums[i];      }     return nums[nums.size()-1];    }};