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

# Challenge Notebook¶

## Constraints¶

• Can we assume this is a stack of ints?
• Yes
• Can we assume the input values for push are valid?
• Yes
• If we call this function on an empty stack, can we return sys.maxsize?
• Yes
• Can we assume we already have a stack class that can be used for this problem?
• Yes
• Can we assume this fits memory?
• Yes

## Test Cases¶

• Push/pop on empty stack
• Push/pop on non-empty stack
• Min on empty stack
• Min on non-empty 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 [ ]:
%run ../stack/stack.py

In [ ]:
import sys

class StackMin(Stack):

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

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

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

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


## Unit Test¶

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

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

class TestStackMin(unittest.TestCase):

def test_stack_min(self):
print('Test: Push on empty stack, non-empty stack')
stack = StackMin()
stack.push(5)
self.assertEqual(stack.peek(), 5)
self.assertEqual(stack.minimum(), 5)
stack.push(1)
self.assertEqual(stack.peek(), 1)
self.assertEqual(stack.minimum(), 1)
stack.push(3)
self.assertEqual(stack.peek(), 3)
self.assertEqual(stack.minimum(), 1)
stack.push(0)
self.assertEqual(stack.peek(), 0)
self.assertEqual(stack.minimum(), 0)

print('Test: Pop on non-empty stack')
self.assertEqual(stack.pop(), 0)
self.assertEqual(stack.minimum(), 1)
self.assertEqual(stack.pop(), 3)
self.assertEqual(stack.minimum(), 1)
self.assertEqual(stack.pop(), 1)
self.assertEqual(stack.minimum(), 5)
self.assertEqual(stack.pop(), 5)
self.assertEqual(stack.minimum(), sys.maxsize)

print('Test: Pop empty stack')
self.assertEqual(stack.pop(), None)

print('Success: test_stack_min')

def main():
test = TestStackMin()
test.test_stack_min()

if __name__ == '__main__':
main()


## Solution Notebook¶

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