[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;
}
}