ASP 8 Queens solution

To find the solutions to the 8 queens puzzle. The puzzle asks "How can you place 8 Queens on a chess board so that no Queen can attack any other queen?"

Original Author: Richard Lindsay

Inputs

All the user has to input is the number of solutions they would like to see. (There are 92 possible ways to arrange 8Queens on a chess board so that no Queen can attack any other queen.

Assumptions

A recursive Algorithm is used. I copied my own VB code (also available on PlanetSourceCode) Only minor changes were required to run it as ASP. I generally do the "Hello World" exercise then I use the 8 Queens puzzle as my way of learning any new programming language. It forces me to learn most of the basic language structures (multi dimentional arrays, Functions, Display and/or printing, getting input etc.) By the time I finish the 8 Queens puzzle I usually feel pretty comfortable with a new language.

Returns

The result is a series of graphical displays that show how to arrange 8 Queens on a chess board so that no Queen can attack any other queen.

Side Affects

There are nearly 17,000,000 different ways to arrange 8 Queens on a chess board so if you ask to see all 92 solutions this code has to try them all. On a slower computer that can take 2 or 3 minutes since this is a script not compiled code.

Code

<%@ LANGUAGE=VBScript %> <% Server.ScriptTimeOut=200 %> <% If Request.Form("NumSolutions") = "" Then %>


This web page can show you all the solutions to the 8-Queens puzzle. There are 92 
possible solutions. Please enter the number of solutions you would like to see then 
click the submit button.


This demonstrates the use of functions in an ASP page. A recursive algorithim 
is used to solve the problem. If you are familiar with VB and want to do a compairison
you can look at my 8 Queens solution in the VB section of www.planetsourcecode.com. 
This is almost a pure cut and paste. It only took about 10 minutes to make it into 
an ASP application. The only real changes are in the Sub UpdateDisplay() other than 
that all I did was delete all the data typing since in VBScript everything is a Variant.




<% Else %>
<%
Dim NumToFind
Dim mblnBoard(7, 7)
Dim solutions
NumToFind = Request.Form ("NumSolutions")
bln8Queens(0)
Function blnCheckUp(ByVal intRow, ByVal intColumn) 
blnCheckUp = True
Do Until intRow = 0 Or intColumn = 0
  intRow = intRow - 1
  intColumn = intColumn - 1
  If mblnBoard(intRow, intColumn) Then
    blnCheckUp = False
    Exit Function
  End If
Loop
End Function
Function blnCheckDown(ByVal intRow, ByVal intColumn) 
blnCheckDown = True
Do Until intRow = 7 Or intColumn = 0
  intRow = intRow + 1
  intColumn = intColumn - 1
  If mblnBoard(intRow, intColumn) Then
    blnCheckDown = False
    Exit Function
  End If
Loop
End Function
Function blnCheckAcross(ByVal intRow, ByVal intColumn) 
blnCheckAcross = True
Do Until intColumn = 0
  intColumn = intColumn - 1
  If mblnBoard(intRow, intColumn) Then
    blnCheckAcross = False
    Exit Function
  End If
Loop
End Function
Function blnIsSafe(ByVal intRow, ByVal intColumn) 
  blnIsSafe = blnCheckUp(intRow, intColumn) And blnCheckDown(intRow, intColumn) And blnCheckAcross(intRow, intColumn)
End Function
Sub UpdateDisplay()
	Dim intRow
	Dim intColumn 
	Response.Write "
Solution #" & solutions & "
"
	Response.Write ""
	For intRow = 0 to 7
		Response.Write ""
		For intColumn = 0 to 7
			If (intColumn + intRow) MOD 2 = 1 Then
				Response.Write ""
			Else
				Response.Write ">   "
			End If
		Next
		Response.Write ""
	Next
	Response.Write "			Else
				Response.Write "			End If
			If mblnBoard(intRow,intColumn) = True Then
				Response.Write " align=center> Q 











"
End Sub
Function bln8Queens(ByVal intColumn) 
  Dim intRow
  Do
    If intColumn = 7 And blnIsSafe(intRow, intColumn) Then
      mblnBoard(intRow, intColumn) = True
	  solutions = solutions + 1
      UpdateDisplay 
      If CInt(solutions) >= CInt(Request.Form ("NumSolutions")) Then 
		bln8Queens = True
        mblnBoard(intRow, intColumn) = False
        Exit Function 
      End If
      mblnBoard(intRow, intColumn) = False
      intRow = intRow + 1
    Else 
      If blnIsSafe(intRow, intColumn) Then 
        mblnBoard(intRow, intColumn) = True 
        bln8Queens = bln8Queens(intColumn + 1)
        mblnBoard(intRow, intColumn) = False
      End If 
      intRow = intRow + 1 
    End If
  Loop Until bln8Queens = True Or intRow = 8 
End Function
%>
<% End If %>

About this post

Posted: 2002-06-01
By: ArchiveBot
Viewed: 111 times

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