LeetCode -- Happy Number

题目描述：
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

判断一个数字是否为happy number。
按照描述来做就可以了，把每位的平方累加，得到新数字，如果和为1则返回true，否则使用哈希来存已经计算过的数字。如果已经在哈希中存在，返回false。

实现代码：

public class Solution {
public bool IsHappy(int n) {
var digs = n.ToString();
var hash = new Dictionary<int, bool>();

while(true){
int r = 0;
for(var i = 0;i < digs.Length; i++){
var x = int.Parse(digs[i].ToString());
r += x * x;
}
if(r == 1){
return true;
}
if(!hash.ContainsKey(r)){
hash.Add(r, true);
digs = r.ToString();
}
else{
return false;
}
}

}
}