Java Programming--vampire numbers (four-bit) __ programming

Reprint: http://blog.csdn.net/tianmijieguo/article/details/46400911

From "Thinking in Java" (fourth edition) of the 4th chapter of exercise 10 See "Vampire number", the special programming implementation, the following are 3 algorithms (for four-digit) and its comparison:

Let's first explain the vampire numbers: vampire numbers are digits that are even digits, and can be multiplied by a pair of numbers, which is not allowed for numbers that contain the half digits of the product, ending with two 0.

Four-digit Vampire digital example: 1260=21*60,1827=21*87,2187=27*81 ...

First list the results: altogether 7:1260=21*60,1395=15*93,1435=41*35,1530=51*30,1827=87*21,2187=27*81,6880=86*80

Method One:

This method is the official answer to "thinking in Java", because the chapter is very close to the front, so the use of the four-digit traversal method, positive thinking, that is, first four digits, then split, four combination of numbers, if the product is equal to the original number, then output, and calculated as a vampire number.

[Java]  View Plain  copy public class searchforvampirethinkinginjava {          // 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.)       */   //   This method is a straightforward thinking, that is, first four digits, then split, four number combination multiplied, if the product and the original number is equal, then output, And counted as a vampire number. TMJG Add this row and comment   //   The result of Sum is 107,976 times, very large, the algorithm is inefficient, and there is a duplication (6880 = 86 *  80,6880 = 80 * 86). TMJG Add this row and comment                        static int sum=0;//the number of times the call is judged, TMJG add this row and comment                 static int a (int i)  {                    return i/1000;     //for thousand digits, below, TMJG add this line and comment                }                static int b (int  i)  {                    return  (i%1000)/100;                }               static  int c (int i)  {                    return  ((i%1000)%100)/10;                }                static int d (int i)  {                    return  ((i%1000)%100)%10;                }                static int com (int i, int j)  {   //formation 10~ 99 double digits, TMJG add this row and comment                     return  (i * 10)  + j;                }                static void productTest  (int i, int m, int n)  {                     sum++;                    if (m *&Nbsp;n == i)  system.out.println (i +  " = "  + m +  "  *  " + n";               }               public static void  main (String[] args)  {