Category : Miscellaneous Language Source Code
Archive   : XLISP21D.ZIP
Filename : QUEENS2.LSP

 
Output of file : QUEENS2.LSP contained in archive : XLISP21D.ZIP
;
; Place n queens on a board (graphical version)
; See Winston and Horn Ch. 11
;
; Usage:
; (queens )
; where is an integer -- the size of the board - try (queens 4)

; Do two queens threaten each other ?
(defun threat (i j a b)
(or (eql i a) ;Same row
(eql j b) ;Same column
(eql (- i j) (- a b)) ;One diag.
(eql (+ i j) (+ a b)))) ;the other diagonal

; Is poistion (n,m) on the board safe for a queen ?
(defun conflict (n m board)
(cond ((null board) nil)
((threat n m (caar board) (cadar board)) t)
(t (conflict n m (cdr board)))))


; Place queens on a board of size SIZE
(defun queens (size)
(prog (n m board soln)
(setq soln 0) ;Solution #
(setq board nil)
(setq n 1) ;Try the first row
loop-n
(setq m 1) ;Column 1
loop-m
(cond ((conflict n m board) (go un-do-m))) ;Check for conflict
(setq board (cons (list n m) board)) ; Add queen to board
(cond ((> (setq n (1+ n)) size) ; Placed N queens ?
(print-board (reverse board) (setq soln (1+ soln))))) ; Print it
(go loop-n) ; Next row which column?
un-do-n
(cond ((null board) (return 'Done)) ; Tried all possibilities
(t (setq m (cadar board)) ; No, Undo last queen placed
(setq n (caar board))
(setq board (cdr board))))

un-do-m
(cond ((> (setq m (1+ m)) size) ; Go try next column
(go un-do-n))
(t (go loop-m)))))


;Print a board
(defun print-board (board soln &aux size)
(setq size (length board)) ;we can find our own size
(format t "\t\tSolution ~s\n\n\t" soln)
(print-header size 1)
(print-board-aux board size)
(terpri))

; Put Column #'s on top
(defun print-header (size n)
(dotimes (i size) (format t "~s " i))
(terpri))

(defun print-board-aux (board size &aux (row 0))
(mapc #'(lambda (x)
(format t "~s\t" (setq row (1+ row)))
(print-board-row (cadr x) size))
board))

(defun print-board-row (column size)
(dotimes (i size) (princ (if (eql column i) "Q " ". ")))
(terpri))


  3 Responses to “Category : Miscellaneous Language Source Code
Archive   : XLISP21D.ZIP
Filename : QUEENS2.LSP

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

  2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

  3. But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/