Implement the Tower of Hanoi Algorithm - Implement the Tower of Hanoi Algorithm

Python
1

Tell us what’s happening:

Hello, I am confused about why my code says hanoi_solver does not return a string.

I have tried isinstance and it returned true.

Thank you for all the time and help. Ik my is probably not great, recursion is hard. I prob should of used iteration instead.

Your code so far

first_ring = []
second_ring = []
third_ring = []
print_message = ''
initialized = False
def pm(source, target):
    global print_message, first_ring, second_ring, third_ring
    if source == 1:
        ring = first_ring.pop()
    elif source == 2:
        ring = second_ring.pop()
    else:
        ring = third_ring.pop()
    if target == 1:
        first_ring.append(ring)
    elif target == 2:
        second_ring.append(ring)
    else:
        third_ring.append(ring)
    print_message += f'{first_ring} {second_ring} {third_ring} \n'
def solver(n, location = 1, target = 3):
    global first_ring, second_ring, third_ring, print_message, initialized
    if not initialized:
        first_ring = list(range(n, 0, -1))
        second_ring = []
        third_ring = []
        print_message = f'{first_ring} {second_ring} {third_ring} \n'
        initialized = True
    if n == 1:
        pm(location, target)
    else:
        other = 6 - location - target
        solver(n-1, location, other)
        pm(location, target)
        solver(n-1, other, target)
def hanoi_solver(n):
    solver(n)
    return str(print_message.rstrip('\n'))
print(hanoi_solver(4))

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/147.0.0.0 Safari/537.36

Challenge Information:

Implement the Tower of Hanoi Algorithm - Implement the Tower of Hanoi Algorithm

2

The issue likely comes from using global variables to keep result and intermediate calculations. This effectively causes hanoi_solver to be usable only single time.

Take a look when there’s more than one calls below the code:

print(hanoi_solver(2))
print(hanoi_solver(3))

It ends up with exception:

IndexError: pop from empty list