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;;; hanoi.el --- towers of hanoi in GNUmacs
; Author (a) 1985, Damon Anton Permezel
;;;
;;; hanoi-topos - direct cursor addressing
;;;
(defun hanoi-topos (row col)
(goto-line row)
(beginning-of-line)
(forward-char col))
;;;
;;; hanoi - user callable Towers of Hanoi
;;;
;;;###autoload
(defun hanoi (nrings)
"Towers of Hanoi diversion. Argument is number of rings."
(interactive
(list (if (null current-prefix-arg)
3
(prefix-numeric-value current-prefix-arg))))
(if (<= nrings 0) (error "Negative number of rings"))
(let (pole-spacing
floor-row
fly-row
(window-height (window-height (selected-window)))
(window-width (window-width (selected-window))))
(let ((h (+ nrings 2))
(w (+ (* (1- nrings) 6) 2 5)))
(if (not (and (>= window-width h)
(> window-width w)))
(progn
(delete-other-windows)
(if (not (and (>= (setq window-height
(window-height (selected-window))) h)
(> (setq window-width
(window-width (selected-window))) w)))
(error "Screen is too small (need at least %dx%d)" w h))))
(setq pole-spacing (/ window-width 6))
(if (not (zerop (logand pole-spacing 1)))
;; must be even
(setq pole-spacing (1+ pole-spacing)))
(setq floor-row (if (> (- window-height 3) h)
(- window-height 3) window-height)))
(let ((fly-row (- floor-row nrings 1))
;; pole: column . fill height
(pole-1 (cons pole-spacing floor-row))
(pole-2 (cons (* 3 pole-spacing) floor-row))
(pole-3 (cons (* 5 pole-spacing) floor-row))
(rings (make-vector nrings nil)))
;; construct the ring list
(let ((i 0))
(while (< i nrings)
;; ring: [pole-number string empty-string]
(aset rings i (vector nil
(make-string (+ i i 3) (+ ?0 i))
(make-string (+ i i 3) ?\ )))
(setq i (1+ i))))
;;
;; init the screen
;;
(switch-to-buffer "*Hanoi*")
(setq buffer-read-only nil)
(buffer-disable-undo (current-buffer))
(erase-buffer)
(let ((i 0))
(while (< i floor-row)
(setq i (1+ i))
(insert-char ?\ (1- window-width))
(insert ?\n)))
(insert-char ?= (1- window-width))
(let ((n 1))
(while (< n 6)
(hanoi-topos fly-row (* n pole-spacing))
(setq n (+ n 2))
(let ((i fly-row))
(while (< i floor-row)
(setq i (1+ i))
(next-line 1)
(insert ?\|)
(delete-char 1)
(backward-char 1)))))
;(sit-for 0)
;;
;; now draw the rings in their initial positions
;;
(let ((i 0)
ring)
(while (< i nrings)
(setq ring (aref rings (- nrings 1 i)))
(aset ring 0 (- floor-row i))
(hanoi-topos (cdr pole-1)
(- (car pole-1) (- nrings i)))
(hanoi-draw-ring ring t nil)
(setcdr pole-1 (1- (cdr pole-1)))
(setq i (1+ i))))
(setq buffer-read-only t)
(sit-for 0)
;;
;; do it!
;;
(hanoi0 (1- nrings) pole-1 pole-2 pole-3)
(goto-char (point-min))
(message "Done")
(setq buffer-read-only t)
(set-buffer-modified-p (buffer-modified-p))
(sit-for 0))))
;;;
;;; hanoi0 - work horse of hanoi
;;;
(defun hanoi0 (n from to work)
(cond ((input-pending-p)
(signal 'quit (list "I can tell you've had enough")))
((< n 0))
(t
(hanoi0 (1- n) from work to)
(hanoi-move-ring n from to)
(hanoi0 (1- n) work to from))))
;;;
;;; hanoi-move-ring - move ring 'n' from 'from' to 'to'
;;;
;;;
(defun hanoi-move-ring (n from to)
(let ((ring (aref rings n)) ; ring <- ring: (ring# . row)
(buffer-read-only nil))
(let ((row (aref ring 0)) ; row <- row ring is on
(col (- (car from) n 1)) ; col <- left edge of ring
(dst-col (- (car to) n 1)) ; dst-col <- dest col for left edge
(dst-row (cdr to))) ; dst-row <- dest row for ring
(hanoi-topos row col)
(while (> row fly-row) ; move up to the fly row
(hanoi-draw-ring ring nil t) ; blank out ring
(previous-line 1) ; move up a line
(hanoi-draw-ring ring t nil) ; redraw
(sit-for 0)
(setq row (1- row)))
(setcdr from (1+ (cdr from))) ; adjust top row
;;
;; fly the ring over to the right pole
;;
(while (not (equal dst-col col))
(cond ((> dst-col col) ; dst-col > col: right shift
(end-of-line 1)
(delete-backward-char 2)
(beginning-of-line 1)
(insert ?\ ?\ )
(sit-for 0)
(setq col (1+ (1+ col))))
((< dst-col col) ; dst-col < col: left shift
(beginning-of-line 1)
(delete-char 2)
(end-of-line 1)
(insert ?\ ?\ )
(sit-for 0)
(setq col (1- (1- col))))))
;;
;; let the ring float down
;;
(hanoi-topos fly-row dst-col)
(while (< row dst-row) ; move down to the dest row
(hanoi-draw-ring ring nil (> row fly-row)) ; blank out ring
(next-line 1) ; move down a line
(hanoi-draw-ring ring t nil) ; redraw ring
(sit-for 0)
(setq row (1+ row)))
(aset ring 0 dst-row)
(setcdr to (1- (cdr to)))))) ; adjust top row
;;;
;;; draw-ring - draw the ring at point, leave point unchanged
;;;
;;; Input:
;;; ring
;;; f1 - flag: t -> draw, nil -> erase
;;; f2 - flag: t -> erasing and need to draw ?\|
;;;
(defun hanoi-draw-ring (ring f1 f2)
(save-excursion
(let* ((string (if f1 (aref ring 1) (aref ring 2)))
(len (length string)))
(delete-char len)
(insert string)
(if f2
(progn
(backward-char (/ (+ len 1) 2))
(delete-char 1) (insert ?\|))))))
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