吸血鬼数字算法

转载自 http://yangl.iteye.com/blog/264634

package org.idcn.jse;

public class XiXieGui {
/**
 * 吸血鬼数字算法
 * 如：12*60=1260
 * YangL.
 */
public static void main(String[] args) {
String[] ar_str1, ar_str2;
int sum = 0;
for (int i = 10; i < 100; i++) {
for (int j = i + 1; j < 100; j++) {
int i_val = i * j;
if (i_val < 1000 || i_val > 9999)
continue; // 积小于1000或大于9999排除,继续下一轮环
ar_str1 = String.valueOf(i_val).split("");
ar_str2 = (String.valueOf(i) + String.valueOf(j)).split("");
java.util.Arrays.sort(ar_str1);
java.util.Arrays.sort(ar_str2);
if (java.util.Arrays.equals(ar_str1, ar_str2)) {
// 排序后比较,为真则找到一组
sum++;
System.out.println("第" + sum + "组: " + i + "*" + j + "="
+ i_val);
}
}
}
System.out.println("共找到" + sum + "组吸血鬼数");
}
}

这个算法应该是比较简单的了。算法中用到String.valueOf(j)).split("");的方法来把数字转换为字符串，以拆分数字的方法用的很巧妙了。把数字的比较，转换为对字符串的比较，实在高明。

下面是我在《Thinking in Java, 2nd edition, Annotated Solution Guide Revision 1.0》中找到的答案，也就是Thinking in JAVA的官方答案书上的答案。不过个人感觉没有上面的算法好。

//: c03:E11_Vampire.java
// Solution by Dan Forhan
import java.applet.*;
import java.awt.*;

publicclass Vampire extends Applet {
    privateint num1, num2, product;
    privateint[] startDigit = newint[4];
    privateint[] productDigit = newint[4];
    privateint count = 0;
    privateint vampCount = 0;
    privateint x, y;
    publicvoid paint(Graphics g) {
      g.drawString("Vampire Numbers", 10, 20);
      g.drawLine(10, 22, 150, 22);
      // Positioning for output to applet:
      int column = 10, row = 35;
      for(num1 = 10; num1 <= 99; num1++)
        for(num2 = 10; num2 <= 99; num2++) {
          product = num1 * num2;
          startDigit[0] = num1 / 10;
          startDigit[1] = num1 % 10;
          startDigit[2] = num2 / 10;
          startDigit[3] = num2 % 10;
          productDigit[0] = product / 1000;
          productDigit[1] = (product % 1000) / 100;
          productDigit[2] = product % 1000 % 100/10;
          productDigit[3] = product % 1000 % 100%10;
          count = 0;
          for(x = 0; x < 4; x++)
            for(y = 0; y < 4; y++) {
              if (productDigit[x] == startDigit[y]){
                count++;
                productDigit[x] = -1;
                startDigit[y] = -2;
                if (count == 4) {
                  vampCount++;
                  int a = (int)Math.random() * 100;
                  int b = (int)Math.random() * 100;
                  int c = (int)Math.random() * 100;
                  if (vampCount < 10) {
                    g.drawString("Vampire number     "
                      + vampCount + " is " + num1 +
                      " * " + num2 + " = "+ product,
                      column, row);
                    row += 20;
                  } else {
                    g.drawString("Vampire number    "
                      + vampCount + " is " + num1 +
                      " * " + num2 + " = "+ product,
                      column, row);
                    row += 20;
                  }
                }
              }
            }
        }
    }
} ///:~