LeetCode: 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) {        if (n < 1) return false;        if (n == 1) return true;                unordered_set<int> appear;        appear.insert(n);        int sum = 0;                while(sum != 1) {            while(n != 0) {                sum += (n % 10) * (n % 10);                n /= 10;            }                        if (sum == 1) return true;            else {                if (appear.find(sum) != appear.end()) return false;            }            appear.insert(sum);            n = sum;            sum = 0;        }                return true;    }};