136. Single Number

problem description

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

algorithm thought

使用异或的性质，两个同样的数，异或之后结果相同。所以将所有数异或就行

code

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int res=0;
        for(auto num:nums){
            res^=num;
        }
        return res;
    }
};

algorithm analysis

两个数异或时间复杂度O(1)，遍历一遍出结果，时间复杂度O(n)