HappyNum

/*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*/

import java.util.*;

public class HappyNum {

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        System.out.println(isHappy(19));

    }

    /**

     * @param n

     */

    public static int pingfanghe(int n) {

        int sum = 0;

        while (n != 0) {

            sum += (n % 10) * (n % 10);

            n = n / 10;

        }

        return sum;

    }

    public static boolean isHappy(int n) {

        /*

         * int sum=0; char[] ch=String.valueOf(n).toCharArray(); for(int

         * i=0;i<ch.length;i++) sum+=(ch[i])*ch[i]; //这样不行，返回的是asc码

         * System.out.println(sum); if(n==1) return true; else return

         * isHappy(n);

         */

        /*

         * if(n==1) return true; Set<Integer> al=new HashSet<Integer>(); int

         * sum=0; while(n!=0) { al.add(n%10); n=n/10; } System.out.println(al);

         * for(int i=0;i<al.size();i++) sum+=al.*al.get(i); n=sum;

         * System.out.println(n);

         *

         *

         *

         * // return isHappy(n);

         *

         * return isHappy(n);

         */

        Set<Integer> hs = new HashSet<Integer>();

        while (true) {

            if (hs.contains(n))

                return false;

            if (n == 1)

                return true;

            hs.add(n);

            n = pingfanghe(n);

        }

    }

}

注意：1.循环的判断

2.字符数组转化是不行的，输出的是asc码。

3.集合框架的使用