leetcode 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: 19 is a happy number

12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

class Solution {
public:
    bool isHappy(int n) {
        unordered_map<int, int> mp;
        mp.insert({n, 1});
        for (;;) {
            int sum = 0;
            while(n > 0) {
                int x = n % 10;
                n /= 10;
                sum += x*x;
            }
            //cout << "sum " << sum << endl;
            if (sum == 1) return true;
            if (mp.count(sum) > 0 ) return false;
            mp.insert({sum,1});
            n = sum;
            //cout << n << endl;
        }
        return false;
    }
};