TIJ4 Chapter Control, Exercise 10, page 154

吸血鬼数字

// control/VampireNumbers.java
// TIJ4 Chapter Control, Exercise 10, page 154
/* A vampire number has an even number of digits and is formed by multiplying a
* pair of numbers containing half the number of digits of the result. The
* digits are taken from the original number in any order. Pairs of trailing
* zeroes are not allowed. Examples include: 1260 = 21 * 60, 1827 = 21 * 87,
* 2187 = 27  * 81. Write a program that finds all the 4-digit vampire numbers.
* (Suggested by Dan Forhan.)
*/ 

package com.controllingExecution;

import java.util.Arrays;
import java.util.TreeSet;
import java.util.Set;

public class VampireNumbers
{
    
    
    public static void main(String[] args)
    {
    
    
        int a1, a2, result;
        int[] results = new int[14];
        int i = 0;
        for (a1 = 10; a1 < 100; a1++)
        {
    
    
            for (a2 = 10; a2 < 100; a2++)
            {
    
    
                result = a1 * a2;
                String[] a = String.valueOf(result).split("");
                String[] b = String.valueOf(a1 + "" + a2).split("");
                Arrays.sort(a);
                Arrays.sort(b);
                if (Arrays.equals(a, b))
                    results[i++] = result;
            }
        }

        Set<Integer> set = new TreeSet<Integer>();
        for (int m : results)
            set.add(m);
        Integer[] results2 = set.toArray(new Integer[0]);
        System.out.println(Arrays.toString(results2));//[1260, 1395, 1435, 1530, 1827, 2187, 6880]

    }
}