LeetCode -- Happy Number

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題目描述：
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




判斷一個數字是否為happy number。
按照描述來做就可以了，把每位的平方累加，得到新數字，如果和為1則返回true，否則使用雜湊來存已經計算過的數字。如果已經在雜湊中存在，返回false。


實現代碼：

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;    }    }    }}

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LeetCode -- Happy Number