1.136题
https://leetcode-cn.com/problems/single-number/

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

2.https://leetcode-cn.com/problems/single-number-iii/ 260题

class Solution {
public:
    vector<int> singleNumber(vector<int>& nums) {
        int ab=0;
        for(auto x:nums) ab=ab^x; //a^b

        int k=0;
        while((ab>>k&1)==0) k++;

        int a=0;

        for(auto x:nums)
        {
            if(x>>k&1)  a=a^x;
        }
        return {a,ab^a};
    }
};

3.https://leetcode-cn.com/problems/single-number-ii/
137

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int one=0,two=0;
        for(auto x:nums)
        {
            one=(one^x)&(~two);
            two=(two^x)&(~one);
        }
        return one;

    }
};