vampirenumbers.java

JAVA编程思想第四版英文原版习题答案. pdf原版的

// 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.)
*/ 

public class VampireNumbers {	
		static int a(int i) {
			return i/1000;
		}
		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) {
			return (i * 10) + j;
		}
		static void productTest (int i, int m, int n) {
			if(m * n == i) System.out.println(i + " = " + m + " * " + n);
		}	
	public static void main(String[] args) {		
		for(int i = 1001; i < 9999; i++) {			
			productTest(i, com(a(i), b(i)), com(c(i), d(i)));
			productTest(i, com(a(i), b(i)), com(d(i), c(i)));
			productTest(i, com(a(i), c(i)), com(b(i), d(i)));
			productTest(i, com(a(i), c(i)), com(d(i), b(i)));
			productTest(i, com(a(i), d(i)), com(b(i), c(i)));
			productTest(i, com(a(i), d(i)), com(c(i), b(i)));
			productTest(i, com(b(i), a(i)), com(c(i), d(i)));
			productTest(i, com(b(i), a(i)), com(d(i), c(i)));
			productTest(i, com(b(i), c(i)), com(d(i), a(i)));
			productTest(i, com(b(i), d(i)), com(c(i), a(i)));
			productTest(i, com(c(i), a(i)), com(d(i), b(i)));
			productTest(i, com(c(i), b(i)), com(d(i), a(i)));
		}			
	} 
}