Happy Number

LeetCode原题：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

主要内容：判断给定数是否符合条件

解题思想：除了会出现结果等于1的情况还会出现无限循环，要得出是否是无限循环从而得出否定的结论需要判断该循环是否属于有限循环（该类判断方法的循环类别）

参考C++代码：

class Solution {
public:
    int med(int n) {
        int b = 0;
        int c = 0;
        while(n != 0) {
            b = n % 10;
            c = c + b * b;
            n = n / 10;
        }
        return c;
    }
    bool isHappy(int n) {
        int b = n;
        set<int> s;
        while (med(b) != 1) {
            if (s.count(b)) {
                return false;
            } else {
                s.insert(b);
            }
            b =  med(b);
        }
        return true;
    }
};