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

Challenge Notebook¶

Constraints¶

• If we pop on an empty stack, do we return None?
• Yes
• Can we assume this fits memory?
• Yes

Test Cases¶

Push¶

• Push to empty stack
• Push to non-empty stack

Pop¶

• Pop on empty stack
• Pop on single element stack
• Pop on multiple element stack

Peek¶

• Peek on empty stack
• Peek on one or more element stack

Is Empty¶

• Is empty on empty stack
• Is empty on one or more element stack

Algorithm¶

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.

Code¶

In [ ]:
class Node(object):

def __init__(self, data):
# TODO: Implement me
pass

class Stack(object):

def __init__(self, top=None):
# TODO: Implement me
pass

def push(self, data):
# TODO: Implement me
pass

def pop(self):
# TODO: Implement me
pass

def peek(self):
# TODO: Implement me
pass

def is_empty(self):
# TODO: Implement me
pass


Unit Test¶

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

In [ ]:
# %load test_stack.py
import unittest

class TestStack(unittest.TestCase):

# TODO: It would be better if we had unit tests for each
# method in addition to the following end-to-end test
def test_end_to_end(self):
print('Test: Empty stack')
stack = Stack()
self.assertEqual(stack.peek(), None)
self.assertEqual(stack.pop(), None)

print('Test: One element')
top = Node(5)
stack = Stack(top)
self.assertEqual(stack.pop(), 5)
self.assertEqual(stack.peek(), None)

print('Test: More than one element')
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)
self.assertEqual(stack.pop(), 3)
self.assertEqual(stack.peek(), 2)
self.assertEqual(stack.pop(), 2)
self.assertEqual(stack.peek(), 1)
self.assertEqual(stack.is_empty(), False)
self.assertEqual(stack.pop(), 1)
self.assertEqual(stack.peek(), None)
self.assertEqual(stack.is_empty(), True)

print('Success: test_end_to_end')

def main():
test = TestStack()
test.test_end_to_end()

if __name__ == '__main__':
main()


Solution Notebook¶

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