202. Happy Number

Write an algorithm to determine if a number is "happy".

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

class Solution {
public:
    set<int> map;
    bool isHappy(int n) {
        if(map.find(n)==map.end()){
             map.insert(n);
             n =sum(n);
             return isHappy(n);
        } 
        return n==1;
    }
    int sum(int n){
        string s = to_string(n);
        int cnt =0;
        for(int i = 0;i<s.size();i++){  
            int v = s[i] - '0';
            cnt+=v*v;
        }
        return cnt;
    }
};