题目描述：
吸血鬼数字是指位数为偶数的数字，可以由一对数字相乘而得到，
而这对数字各包含乘积的一半位数的数字，其中最初的数字中可以
选取的数字可以任意排序，以两个0结尾的数字是不允许的，例如，下
面的数字都是吸血鬼数字：
1260=21*60
1827=21*87
2187=27*81
编写一个程序，找出4位数的所有吸血鬼数字。
package chapter3_Ex10;
public class Vampire {
public static void main(String[] args){
int[] startDigit=new int[4];
int[] productDigit=new int[4];
for(int num1=10;num1<100;++num1){
for(int num2=num1;num2<100;++num2){
if((num1*num2)%9 != (num1+num2)%9)
continue;
int 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;
int count=0;
for(int i=0;i<4;++i){
for(int j=0;j<4;j++){
if(startDigit[i]==productDigit[j]){
++count;
startDigit[i]=-1;
productDigit[j]=-2;
}
}
}
if(count==4){
System.out.println(num1+" * "+num2+" = "+product);
}
}
}
}
}
运行结果：
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