Happy Number

class Solution {
public:
    bool isHappy(int n) {
        unordered_set<int> num;
        int sum = n;
        do {
            int old = sum;
            num.insert(old);
            sum = 0;
            while (old) {
                int d = old % 10;
                sum += d * d;
                old /= 10;
            }
        } while(!(sum == 1 || num.find(sum) != num.end()));
        
        return sum == 1;
    }
};