leetcode 202. Happy Number

class Solution {
public:
    bool isHappy(int n) {
        if(n <= 0)
            return false;
        set<int> res;
        while(res.count(n) == 0){
            res.insert(n);
            int num = 0;
            while(n != 0){
                num += (n%10)*(n%10);
                n = n/10;
            }
            if(num == 1)
                return true;
            n = num;
        }
        return false;
    }
};

count()用来查找set中某个某个键值出现的次数

https://blog.csdn.net/lym940928/article/details/79671879