vampires number Eckel B. Thinking in Java, Java

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//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_111

import java.util.*;
import java.lang.*;

class Rextester
{  
    public static void main(String args[])
    {
	int ch[]= new int[4];
	int old=0;
	for (int chislo=1001; chislo<9999; chislo++)
	  if (chislo%10!=0) 
	  {
	    ch[0]=Math.round(chislo/1000);
	    ch[1]=Math.round(chislo/100)-ch[0]*10;
	    ch[2]=Math.round(chislo/10)-ch[0]*100-ch[1]*10;
	    ch[3]=chislo-Math.round(chislo/10)*10;
	    for (int a=0;a<4;a++) 
	      for (int b=0;b<4;b++)
		for (int c=0;c<4;c++)
		  for (int d=0;d<4;d++)
		    if ((a!=b)&&(c!=d)&&(b!=c)&&
			(a!=d)&&(a!=c)&&(b!=d)&& 
		    (((ch[a]*10+ch[b])*(ch[c]*10+ch[d]))==chislo))
			{
			if (old!=chislo) 
			{
			System.out.println(chislo+" = "+
			ch[a]+ch[b]+" * "+ch[c]+ch[d]);
			old=chislo;
			}
			}
	    }
    }
}
// Eckel B.  Thinking in Java 
//Еккель Философия Java стр.143 задача 24

/* old version
import java.util.*;
import java.lang.*;

class Rextester
{  
    public static void main(String args[])
    {	for (int chislo=1001; chislo<9999; chislo++)
		if(chislo%10!=0) {
		int ch1=Math.round(chislo/1000);
		int ch2=Math.round(chislo/100)-ch1*10;
		int ch3=Math.round(chislo/10)-ch1*100-ch2*10;
		int ch4=chislo-Math.round(chislo/10)*10;
		int a=((ch1*10+ch2)*(ch3*10+ch4));
		int b=((ch1*10+ch3)*(ch2*10+ch4));
		int c=((ch1*10+ch4)*(ch3*10+ch2));
		int d=((ch4*10+ch1)*(ch2*10+ch3));
		int e=((ch4*10+ch2)*(ch3*10+ch1));
		int f=((ch4*10+ch1)*(ch3*10+ch2));
		int g=((ch3*10+ch1)*(ch2*10+ch4));
		int h=((ch2*10+ch4)*(ch3*10+ch1));
		if (a==chislo)
System.out.println(chislo+" "+ch1+ch2+" * "+ch3+ch4);
		else if ( b==chislo)
System.out.println(chislo+" "+ch1+ch3+" * "+ch2+ch4);
		else if (c==chislo)	
System.out.println(chislo+" "+ch1+ch4+" * "+ch3+ch2);
		else if (d==chislo)	
System.out.println(chislo+" "+ch4+ch3+" * "+ch2+ch1);
		else if (e==chislo)	
System.out.println(chislo+" "+ch4+ch2+" * "+ch3+ch1);
		else if (f==chislo)	
System.out.println(chislo+" "+ch4+ch1+" * "+ch3+ch2);
		else if (g==chislo)	
System.out.println(chislo+" "+ch3+ch1+" * "+ch2+ch4);
		else if (h==chislo)	
System.out.println(chislo+" "+ch2+ch4+" * "+ch3+ch1);
		}
    }
}
*/

[ + ] Show input
Compilation time: 1.13 sec, absolute running time: 0.21 sec, cpu time: 0.3 sec, memory peak: 30 Mb, absolute service time: 1,53 sec