[LeetCode 解题报告]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:
    bool isHappy(int n) {
        unordered_set<int> s;
        while (n != 1) {
            n = sum(n);
            if (s.count(n))
                break;
            s.insert(n);
        }
        return n == 1 ? true : false;
    }
    
    static int sum(int n) {
        int res = 0;
        while (n) {
            res += pow(n%10, 2);
            n /= 10;
        }
        return res;
    }
};