• TowersOfHanoi

Towers of Hanoi by Guido van Rossum

# hanoi.py
# Animated Towers of Hanoi using Tk with optional bitmap file in
# background.
#
# Usage: tkhanoi [n [bitmapfile]]
#
# n is the number of pieces to animate; default is 4, maximum 15.
#
# The bitmap file can be any X11 bitmap file (look in
# /usr/include/X11/bitmaps for samples); it is displayed as the
# background of the animation.  Default is no bitmap.

# This uses Steen Lumholt's Tk interface
from Tkinter import *

# Basic Towers-of-Hanoi algorithm: move n pieces from a to b, using c
# as temporary.  For each move, call report()
def hanoi(n, a, b, c, report):
        if n <= 0: return
        hanoi(n-1, a, c, b, report)
        report(n, a, b)
        hanoi(n-1, c, b, a, report)

# The graphical interface
class Tkhanoi:

        # Create our objects
        def __init__(self, n, bitmap = None):
                self.n = n
                self.tk = tk = Tk()
                self.canvas = c = Canvas(tk)
                c.pack()
                width, height = tk.getint(c['width']), tk.getint(c['height'])

                # Add background bitmap
                if bitmap:
                        self.bitmap = c.create_bitmap(width/2, height/2,
                                                      {'bitmap': bitmap,
                                                       'foreground': 'blue'})

                # Generate pegs
                pegwidth = 10
                pegheight = height/2
                pegdist = width/3
                x1, y1 = (pegdist-pegwidth)/2, height*1/3
                x2, y2 = x1+pegwidth, y1+pegheight
                self.pegs = []
                p = c.create_rectangle(x1, y1, x2, y2, {'fill': 'black'})
                self.pegs.append(p)
                x1, x2 = x1+pegdist, x2+pegdist
                p = c.create_rectangle(x1, y1, x2, y2, {'fill': 'black'})
                self.pegs.append(p)
                x1, x2 = x1+pegdist, x2+pegdist
                p = c.create_rectangle(x1, y1, x2, y2, {'fill': 'black'})
                self.pegs.append(p)
                self.tk.update()

                # Generate pieces
                pieceheight = pegheight/16
                maxpiecewidth = pegdist*2/3
                minpiecewidth = 2*pegwidth
                self.pegstate = [[], [], []]
                self.pieces = {}
                x1, y1 = (pegdist-maxpiecewidth)/2, y2-pieceheight-2
                x2, y2 = x1+maxpiecewidth, y1+pieceheight
                dx = (maxpiecewidth-minpiecewidth) / (2*max(1, n-1))
                for i in range(n, 0, -1):
                        p = c.create_rectangle(x1, y1, x2, y2,
                                               {'fill': 'red'})
                        self.pieces[i] = p
                        self.pegstate[0].append(i)
                        x1, x2 = x1 + dx, x2-dx
                        y1, y2 = y1 - pieceheight-2, y2-pieceheight-2
                        self.tk.update()
                        self.tk.after(25)

        # Run -- never returns
        def run(self):
                hanoi(self.n, 0, 1, 2, self.report)
                self.tk.mainloop() # Hang around...

        # Reporting callback for the actual hanoi function
        def report(self, i, a, b):
                if self.pegstate[a][-1] != i: raise RuntimeError # Assertion
                del self.pegstate[a][-1]
                p = self.pieces[i]
                c = self.canvas

                # Lift the piece above peg a
                ax1, ay1, ax2, ay2 = c.bbox(self.pegs[a])
                while 1:
                        x1, y1, x2, y2 = c.bbox(p)
                        if y2 < ay1: break
                        c.move(p, 0, -1)
                        self.tk.update()

                # Move it towards peg b
                bx1, by1, bx2, by2 = c.bbox(self.pegs[b])
                newcenter = (bx1+bx2)/2
                while 1:
                        x1, y1, x2, y2 = c.bbox(p)
                        center = (x1+x2)/2
                        if center == newcenter: break
                        if center > newcenter: c.move(p, -1, 0)
                        else: c.move(p, 1, 0)
                        self.tk.update()

                # Move it down on top of the previous piece
                pieceheight = y2-y1-2
                newbottom = by2 - pieceheight*len(self.pegstate[b]) - 2
                while 1:
                        x1, y1, x2, y2 = c.bbox(p)
                        if y2 >= newbottom: break
                        c.move(p, 0, 1)
                        self.tk.update()

                # Update peg state
                self.pegstate[b].append(i)

# Main program
def main():
        import sys, string

        # First argument is number of pegs, default 4
        if sys.argv[1:]:
                n = string.atoi(sys.argv[1])
        else:
                n = 4

        # Second argument is bitmap file, default none
        if sys.argv[2:]:
                bitmap = sys.argv[2]
                # Reverse meaning of leading '@' compared to Tk
                if bitmap[0] == '@': bitmap = bitmap[1:]
                else: bitmap = '@' + bitmap
        else:
                bitmap = None

        # Create the graphical objects...
        h = Tkhanoi(n, bitmap)

        # ...and run!
        h.run()

# Call main when run as script
if __name__ == '__main__':
        main()