Leetcode 202 Happy Number

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

Solution 1: use hash table to record if duplicate or not. If Duplication is 1 return true, else return zero.

 public class Solution {  
   public boolean isHappy(int n) {  
     Set<Integer> set=new HashSet<>();  
     while (!set.contains(n)) {  
       set.add(n);  
       n=next(n);  
     }  
     if (n==1) return true;  
     return false;  
   }  
   private int next(int x) {  
     int res=0;  
     while (x!=0) {  
       int t=x%10;  
       res+=t*t;  
       x=x/10;  
     }  
     return res;  
   }  
 }