This notebook was prepared by Donne Martin. Source and license info is on GitHub.
We'll use a second stack to keep track of the minimum values.
Complexity:
Complexity:
Complexity:
%run ../stack/stack.py
import sys
class StackMin(Stack):
def __init__(self, top=None):
super(StackMin, self).__init__(top)
self.stack_of_mins = Stack()
def minimum(self):
if self.stack_of_mins.top is None:
return sys.maxsize
else:
return self.stack_of_mins.peek()
def push(self, data):
super(StackMin, self).push(data)
if data < self.minimum():
self.stack_of_mins.push(data)
def pop(self):
data = super(StackMin, self).pop()
if data == self.minimum():
self.stack_of_mins.pop()
return data
%%writefile 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()
Overwriting test_stack_min.py
run -i test_stack_min.py
Test: Push on empty stack, non-empty stack Test: Pop on non-empty stack Test: Pop empty stack Success: test_stack_min