Tower Of Hanoi Problem. Invalid Move

i’ve made it right to the end of this projects but whenever I try to make a move i always get a “invalid move” response. Can’t work this one out at all. Any ideas? thanks :slight_smile:

from stack import Stack

print("\nLet's play Towers of Hanoi!!")

#Create the Stacks
stacks = []
left_stack = Stack("Left")
middle_stack = Stack("Middle")
right_stack = Stack("Right")

stacks += [left_stack, middle_stack, right_stack]

#Set up the Game
num_disks = int(input("\nHow many disks do you want to play with?\n"))
while num_disks < 3:
  num_disks = int(input("Enter a number greater than or equal to 3\n"))
  
for disk in range(num_disks, 0, -1):
  left_stack.push(disk)
  
num_optimal_moves = (2**num_disks) -1
print("\nThe fastest you can solve this game is in {} moves".format(str(num_optimal_moves)))

#Get User Input
def get_input():
  choices = [stack.get_name()[0] for stack in stacks]
  
  while True:
    
    for i in range(len(stacks)):
      name = stacks[i].get_name()
      letter = choices[i]
      print('Enter {0} for {1}'.format(letter, name))
      
    user_input = input('')
      
    if user_input in choices:
      for i in range(len(stacks)):        
        return stacks[i]
    
  

        
#Play the Game

num_user_moves = 0
while right_stack.get_size() != num_disks:
  
  print("\n\n\n...Current Stacks...")
  for stack in stacks:
    stack.print_items()
    
  while True:
    print("\nWhich stack do you want to move from?\n")
    from_stack = get_input()
    
    print("\nWhich stack do you want to move to?\n")   
    to_stack = get_input()
    
    if from_stack.get_size() == 0:
      print ("\n\nInvalid Move. Try Again")
    elif (to_stack.get_size() == 0) or (from_stack.peek() < to_stack.peek()):
      disk = from_stack.pop()
      to_stack.push(disk)
      num_user_moves += 1
      break
    else: 
      print("\n\nInvalid Move. Try Again!")
      
      
print("\n\nYou completed the game in {0} moves, and the optimal number of moves is {1}".format(num_user_moves, num_optimal_moves))
    
      
3 Likes

Hi @willyuma

There is a problem in your get_input function. It contains this statement within a for loop:

        return stacks[i]

That statement should execute only when user_input is equivalent to choices[i]. Use an if statement to ensure that the return statement executes only under that circumstance. Otherwise, it will always execute during the first iteration of the loop.

2 Likes

Thank you! I added a line and it worked! This is a part i struggled on so i used the walkthrough video to go over this and uses the same code as there so i couldn’t work out why it wouldn’t work?

3 Likes

Unfortunately, the walkthrough video omits that if header, as indicated by the screen capture below (made February 20, 2019). Without that test, the function can only return the Stack at index 0 within stacks, which is left_stack, and the user cannot complete a valid move.

3 Likes

ok got it! :slight_smile: thanks

3 Likes