Happy Number

package cn.edu.xidian.sselab.hashtable;

import java.util.HashSet;
import java.util.Set;

/**
*
* @author zhiyong wang
* title： Happy Number
* content:
* 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
*
*        1^2 + 9^2 = 82
*        8^2 + 2^2 = 68
*        6^2 + 8^2 = 100
*        1^2 + 0^2 + 0^2 = 1
*
*
*/
public class HappyNumber {

   //自己改了三次才改正确的方法,出现了两个错误：（1）忘记如果不能于1，会一直循环的情况给排除掉,这里用一个Set保存出现的值来排除这种情况
   //（2）求平方的时候没有用Math.pow(a,b)这种方法
   public boolean isHappy(int n){
       if(n < 1)
           return false;
       Set set = new HashSet();
       while(n > 1){
           if(!set.add(n))
               return false;
           n = calculate(n);
       }
       if(n == 1)
           return true;
       else
           return false;
   }

   private int calculate(int n){
       int result = 0;
       while(n > 0){
           result += Math.pow(n%10, 2);
           n = n/10;
       }
       return result;
   }

}