[LeetCode202]Happy Number判断一个数是不是happy number

题目：

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

中文（把一个正整数各位平方后相加，然后把得到的结果各位平方相加....依次进行下去，如果能得到结果1则是happy number，否则不是）

思路：同计算循环小数一样，把每次计算的结果保存到一个List<int>里，如果出现循环，则返回false即可

代码：

public class Solution {
    public bool IsHappy(int n) {
        int sum = n;
        if(n <= 0)
            return false;
        List<int> appearedNum = new List<int>();
        while(true)
        {
            if(appearedNum.Contains(sum))
                return false;
            else
                appearedNum.Add(sum);
            sum = GetNext(sum);
            if(sum == 1)
                return true;
        }
        return true;
    }
    
    public int GetNext(int num)
    {
        int sum = 0;

        while(num != 0)
        {
            sum += (int)Math.Pow(num % 10, 2);
            num /= 10;
        }
        return sum;
    }
}