?
Solved

8 Queens Problem Recursively

Posted on 1997-11-10
1
Medium Priority
?
1,314 Views
Last Modified: 2012-06-27
Does anyone have an example to solve the 8 Queens problem recursively?

Place 8 queens on a chess board so that no two queens are attacking each other
0
Comment
Question by:sdevine
1 Comment
 
LVL 5

Accepted Solution

by:
y96andha earned 200 total points
ID: 1216722
Here is an example which I just wrote for you. It will lose its indentation when posted, but I hope you can read it anyway. It sets up a chessboard, tries adding a queen at a time in a free position, and for each time marks the squares which cannot be used, and tries to add a new queen recursively.

type
      pos = (Free, Queen, Busy);
      chessboard = array[1..8,1..8] of pos;

Var
  r,k: integer;
  emptyboard : chessboard;

function min(a,b:integer):integer;
begin
      if a<b then min := a else min := b;
end;

function findsolution(board : chessboard; level : Integer): Boolean;
Var
      r,k:integer;
      i:integer;
      ch:char;
      boardcopy:chessboard;
begin
      findsolution:=false;
      boardcopy := board;
      for r:=1 to 8 do
            for k:=1 to 8 do
                  if boardcopy[r, k] = Free Then
                  begin
                        if level+1 = 8 then begin
                              writeln;
                              writeln('Solution:');
                              for r:=1 to 8 do
                              begin
                                    for k:=1 to 8 do
                                          If boardcopy[r, k] = Queen then
                                                write('Q')
                                          else
                                                write(' ');
                                    writeln;
                              end;
                              findsolution:=true;
                              exit;
                        end;


                        board:=boardcopy;
                        for i:=1 to 8 do
                              board[i, k]:=Busy;
                        for i:=1 to 8 do
                              board[r, i]:=Busy;
                        for i:=1-min(r,k) to min(9-r,9-k)-1 do
                              board[r+i, k+i]:=Busy;
                        for i:=1-min(9-r,k) to min(r, 9-k)-1 do
                              board[r-i, k+i]:=Busy;

                        board[r, k]:=Queen;

                        if findsolution(board, level+1) Then
                        begin
                              findsolution:=True;
                              exit;
                        end;

                  end;

end;



begin

      for r:=1 to 8 do
            for k:=1 to 8 do
                  emptyboard[r,k]:=Free;

      if findsolution(emptyboard, 0) then
            writeln('A solution was found');
end.
0

Featured Post

How to Use the Help Bell

Need to boost the visibility of your question for solutions? Use the Experts Exchange Help Bell to confirm priority levels and contact subject-matter experts for question attention.  Check out this how-to article for more information.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Most folks would know the basics of how Dropbox works, so that’s not the purpose of this article. Security is what it’s all about, so here I’ll share how I choose to secure my Dropbox Account and the Data it contains.
In the below post we have mentioned the best hosting type for startups. Also, check out some of the superlative web hosting companies that are proposing affordable web hosting solutions to host your startup website.
Are you ready to place your question in front of subject-matter experts for more timely responses? With the release of Priority Question, Premium Members, Team Accounts and Qualified Experts can now identify the emergent level of their issue, signal…
Whether it be Exchange Server Crash Issues, Dirty Shutdown Errors or Failed to mount error, Stellar Phoenix Mailbox Exchange Recovery has always got your back. With the help of its easy to understand user interface and 3 simple steps recovery proced…
Suggested Courses

862 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question