leetcode 30day--1

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

class Solution {
public:
    //异或 
    // 1 ^ 1 = 0
    int singleNumber(vector<int>& nums) {
        int res = nums[0];
        for(int i=1;i<nums.size();i++){
            res ^= nums[i];
        }
        return res;
    }
};

　　或者利用hash表