This notebook was prepared by Donne Martin. Source and license info is on GitHub.

- Can we assume we already have a stack class that can be used for this problem?
- Yes

- Can we assume the inputs are valid?
- No

- Can we assume this fits memory?
- Yes

- None tower(s) -> Exception
- 0 disks -> None
- 1 disk
- 2 or more disks

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

In [ ]:

```
%run ../../stacks_queues/stack/stack.py
%load ../../stacks_queues/stack/stack.py
```

In [ ]:

```
class Hanoi(object):
def move_disks(self, num_disks, src, dest, buff):
# TODO: Implement me
pass
```

**The following unit test is expected to fail until you solve the challenge.**

In [ ]:

```
# %load test_hanoi.py
import unittest
class TestHanoi(unittest.TestCase):
def test_hanoi(self):
hanoi = Hanoi()
num_disks = 3
src = Stack()
buff = Stack()
dest = Stack()
print('Test: None towers')
self.assertRaises(TypeError, hanoi.move_disks, num_disks, None, None, None)
print('Test: 0 disks')
hanoi.move_disks(num_disks, src, dest, buff)
self.assertEqual(dest.pop(), None)
print('Test: 1 disk')
src.push(5)
hanoi.move_disks(num_disks, src, dest, buff)
self.assertEqual(dest.pop(), 5)
print('Test: 2 or more disks')
for disk_index in range(num_disks, -1, -1):
src.push(disk_index)
hanoi.move_disks(num_disks, src, dest, buff)
for disk_index in range(0, num_disks):
self.assertEqual(dest.pop(), disk_index)
print('Success: test_hanoi')
def main():
test = TestHanoi()
test.test_hanoi()
if __name__ == '__main__':
main()
```

Review the Solution Notebook for a discussion on algorithms and code solutions.