#77
Tower of Hanoi

  1. """The Tower of Hanoi, by Al Sweigart [email protected]
  2. A stack-moving puzzle game.
  3. This code is available at https://nostarch.com/big-book-small-python-programming
  4. Tags: short, game, puzzle"""
  5. 
  6. import copy
  7. import sys
  8. 
  9. TOTAL_DISKS = 5  # More disks means a more difficult puzzle.
 10. 
 11. # Start with all disks on tower A:
 12. COMPLETE_TOWER = list(range(TOTAL_DISKS, 0, -1))
 13. 
 14. 
 15. def main():
 16.     print("""The Tower of Hanoi, by Al Sweigart [email protected]
 17. 
 18. Move the tower of disks, one disk at a time, to another tower. Larger
 19. disks cannot rest on top of a smaller disk.
 20. 
 21. More info at https://en.wikipedia.org/wiki/Tower_of_Hanoi
 22. """
 23.     )
 24. 
 25.     # Set up the towers. The end of the list is the top of the tower.
 26.     towers = {'A': copy.copy(COMPLETE_TOWER), 'B': [], 'C': []}
 27. 
 28.     while True:  # Run a single turn.
 29.         # Display the towers and disks:
 30.         displayTowers(towers)
 31. 
 32.         # Ask the user for a move:
 33.         fromTower, toTower = askForPlayerMove(towers)
 34. 
 35.         # Move the top disk from fromTower to toTower:
 36.         disk = towers[fromTower].pop()
 37.         towers[toTower].append(disk)
 38. 
 39.         # Check if the user has solved the puzzle:
 40.         if COMPLETE_TOWER in (towers['B'], towers['C']):
 41.             displayTowers(towers)  # Display the towers one last time.
 42.             print('You have solved the puzzle! Well done!')
 43.             sys.exit()
 44. 
 45. 
 46. def askForPlayerMove(towers):
 47.     """Asks the player for a move. Returns (fromTower, toTower)."""
 48. 
 49.     while True:  # Keep asking player until they enter a valid move.
 50.         print('Enter the letters of "from" and "to" towers, or QUIT.')
 51.         print('(e.g. AB to moves a disk from tower A to tower B.)')
 52.         response = input('> ').upper().strip()
 53. 
 54.         if response == 'QUIT':
 55.             print('Thanks for playing!')
 56.             sys.exit()
 57. 
 58.         # Make sure the user entered valid tower letters:
 59.         if response not in ('AB', 'AC', 'BA', 'BC', 'CA', 'CB'):
 60.             print('Enter one of AB, AC, BA, BC, CA, or CB.')
 61.             continue  # Ask player again for their move.
 62. 
 63.         # Syntactic sugar - Use more descriptive variable names:
 64.         fromTower, toTower = response[0], response[1]
 65. 
 66.         if len(towers[fromTower]) == 0:
 67.             # The "from" tower cannot be an empty tower:
 68.             print('You selected a tower with no disks.')
 69.             continue  # Ask player again for their move.
 70.         elif len(towers[toTower]) == 0:
 71.             # Any disk can be moved onto an empty "to" tower:
 72.             return fromTower, toTower
 73.         elif towers[toTower][-1] < towers[fromTower][-1]:
 74.             print('Can\'t put larger disks on top of smaller ones.')
 75.             continue  # Ask player again for their move.
 76.         else:
 77.             # This is a valid move, so return the selected towers:
 78.             return fromTower, toTower
 79. 
 80. 
 81. def displayTowers(towers):
 82.     """Display the current state."""
 83. 
 84.     # Display the three towers:
 85.     for level in range(TOTAL_DISKS, -1, -1):
 86.         for tower in (towers['A'], towers['B'], towers['C']):
 87.             if level >= len(tower):
 88.                 displayDisk(0)  # Display the bare pole with no disk.
 89.             else:
 90.                 displayDisk(tower[level])  # Display the disk.
 91.         print()
 92. 
 93.     # Display the tower labels A, B, and C.
 94.     emptySpace = ' ' * (TOTAL_DISKS)
 95.     print('{0} A{0}{0} B{0}{0} C\n'.format(emptySpace))
 96. 
 97. 
 98. def displayDisk(width):
 99.     """Display a disk of the given width. A width of 0 means no disk."""
100.     emptySpace = ' ' * (TOTAL_DISKS - width)
101. 
102.     if width == 0:
103.         # Display a pole segment without a disk:
104.         print(emptySpace + '||' + emptySpace, end='')
105.     else:
106.         # Display the disk:
107.         disk = '@' * width
108.         numLabel = str(width).rjust(2, '_')
109.         print(emptySpace + disk + numLabel + disk + emptySpace, end='')
110. 
111. 
112. # If the program is run (instead of imported), run the game:
113. if __name__ == '__main__':
114.     main()