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import unittest
class Stack(object):
def __init__(self):
"""Initialize an empty stack"""
self.items = []
def push(self, item):
"""Push a new item onto the stack"""
self.items.append(item)
def pop(self):
"""Remove and return the last item"""
# If the stack is empty, return None
# (it would also be reasonable to throw an exception)
if not self.items:
return None
return self.items.pop()
def peek(self):
"""Return the last item without removing it"""
if not self.items:
return None
return self.items[-1]
class MaxStack(object):
# Implement the push, pop, and get_max methods
def __init__(self):
self.m = Stack()
self.stack = Stack()
def push(self, item):
if self.m.peek() is None:
self.m.push(item)
elif item >= self.m.peek():
self.m.push(item)
self.stack.push(item)
def pop(self):
x = self.stack.pop()
if x == self.m.peek():
self.m.pop()
return x
def get_max(self):
return self.m.peek()
################################################################################
# Tests
################################################################################
class Test(unittest.TestCase):
def test_stack_usage(self):
max_stack = MaxStack()
max_stack.push(5)
actual = max_stack.get_max()
expected = 5
self.assertEqual(actual, expected)
max_stack.push(4)
max_stack.push(7)
max_stack.push(7)
max_stack.push(8)
actual = max_stack.get_max()
expected = 8
self.assertEqual(actual, expected)
actual = max_stack.pop()
expected = 8
self.assertEqual(actual, expected)
actual = max_stack.get_max()
expected = 7
self.assertEqual(actual, expected)
actual = max_stack.pop()
expected = 7
self.assertEqual(actual, expected)
actual = max_stack.get_max()
expected = 7
self.assertEqual(actual, expected)
actual = max_stack.pop()
expected = 7
self.assertEqual(actual, expected)
actual = max_stack.get_max()
expected = 5
self.assertEqual(actual, expected)
actual = max_stack.pop()
expected = 4
self.assertEqual(actual, expected)
actual = max_stack.get_max()
expected = 5
self.assertEqual(actual, expected)
unittest.main(verbosity=2)
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