def test_add_first(self):
sll = Singlellist()
self.assertEqual(sll.head, None)
sll.add_first(1)
self.assertEqual(sll.head.value, 1)
sll.add_first(2)
self.assertEqual(sll.head.value, 2)
def test_empty(self):
sll = Singlellist()
self.assertEqual(sll.is_empty(), True)
sll.add_first(1)
self.assertEqual(sll.is_empty(), False)
class LinkedStack(Singlellist):
"""
LIFO Srtack implementation using Python list as underlyinh storage.
"""
def __init__(self):
"""Create and empty stack.
"""
self._data = Singlellist()
def __len__(self):
"""Return the number of elements in the stack.
Time Complexity: O(1)
"""
return len(self._data)
def __repr__(self):
"""
Show the stack properly.
Time Complexity: O(1)
"""
if self.is_empty():
s1 = '| ' + "".center(5) + ' |' + '\n'
s2 = '-' * 9
return s1 + s2
else:
s = []
for i in range(len(self._data) - 1, -1, -1):
ele = self._data[i]
s1 = '| ' + ele.__repr__().center(5) + ' |' + '\n'
s2 = '-' * 9 + '\n'
s.append(s1 + s2)
return ''.join(s)
def is_empty(self):
"""Return True if the stack is empty
Time Complexity: O(1)
"""
return len(self._data) == 0
def push(self, e):
"""Add element to the top of the stack
Time Complexity: O(1)*
Note: "*" in here means amortization
"""
self._data.add_first(e)
def top(self):
"""
Return (but not remove) at the top of the stack.
Raise Empty exception if the stack in empty.
Time Complexity: O(1)
"""
if self.is_empty():
raise Empty("Stack in empty!")
return self._data.head.value
def pop(self):
"""
Remove and return the element from the top of the stack(LIFO)
Raise Empty exception if the stack is empty.
Time Complexity: O(1)*
"""
if self.is_empty():
raise Empty("Stack is empty!")
ele = self._data.head.value
self._data.remove_first()
return ele