[LeetCod] Happy Number

標籤：

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

     個人感覺這道題重點在於，我們用loop迴圈來計算這個數是不是happy number（計算方法很簡單）

     但是如果這個數不是Happy Number，怎樣才能讓這個loop停止呢。

     這裡就可以用到HashSet，當n在計算過程中出現重複的值時，就證明這個數已經不可能是happy number了，我們的loop可以停止了。

     用hashset裡面的contains()method來判斷。（記得add()method一定要放在前面不要末尾哦）n的值也要隨時更新。

     代碼如下。~

public class Solution {    public boolean isHappy(int n) {       if(n==1) return true;       if(n<=0) return false;       int result=0;       HashSet<Integer> hash=new HashSet<Integer>();       while(!hash.contains(n)){           result=0;           hash.add(n);           while(n!=0){               int temp=n%10;               result=result+temp*temp;               n=n/10;           }           n=result;           if(n==1){               return true;           }       }       return false;    }}

 

[LeetCod] Happy Number