202. Happy Number

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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

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

 1 public class Solution {
 2     public boolean isHappy(int n) {
 3         if(n < 0) return false;
 4         HashSet<Integer> hs = new HashSet<Integer>();
 5         int sum = 0;
 6         while(!hs.contains(n)){
 7             if(n == 1){ return true;}
 8             hs.add(n);
 9             while(n!=0){
10                 sum += Math.pow(n%10,2);
11                 n /= 10;
12             }
13             n = sum;
14             sum = 0;
15         }
16         return false;
17     }
18 }

202. Happy Number

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原文地址：http://www.cnblogs.com/guoguolan/p/5396623.html