Towers of Hanoi
In this exercise, you will implement the Towers of Hanoi puzzle with a recursive algorithm. The aim of this game is to transfer all the disks from one of the three rods to another, following these rules:
- You can only move one disk at a time.
- You can only take the upper disk from one of the stacks and place it on top of another stack.
- You cannot put a larger disk on top of a smaller one.
The algorithm shown is an implementation of this game with four disks and three rods called 'A', 'B' and 'C'. The code contains two mistakes. In fact, if you execute it, it crashes the console because it exceeds the maximum recursion depth. Can you find the bugs and fix them?
This exercise is part of the course
Data Structures and Algorithms in Python
Exercise instructions
- Correct the base case.
- Correct the calls to the
hanoi()function.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
def hanoi(num_disks, from_rod, to_rod, aux_rod):
# Correct the base case
if num_disks >= 0:
# Correct the calls to the hanoi function
hanoi(num_disks, from_rod, aux_rod, to_rod)
print("Moving disk", num_disks, "from rod", from_rod,"to rod",to_rod)
hanoi(num_disks, aux_rod, to_rod, from_rod)
num_disks = 4
source_rod = 'A'
auxiliar_rod = 'B'
target_rod = 'C'
hanoi(num_disks, source_rod, target_rod, auxiliar_rod)