def simple_list(n):
"""
Generates simple linked lists with numbers from 0 to n.
Time complexity: O(n)
Space complexity: O(n)
"""
ll = LinkedList()
for i in range(n - 1, -1, -1):
ll.prepend(i)
return ll
class Stack:
def __init__(self):
self.ll = LinkedList()
def push(self, data):
self.ll.prepend(data)
def pop(self):
data = self.ll.head.value
self.ll.delete(0)
return data
def test_prepend(self):
ll = LinkedList()
ll.prepend(1)
self.assertEqual([1], ll.to_list())
ll.prepend(2)
self.assertEqual([2, 1], ll.to_list())
ll.prepend(3)
self.assertEqual([3, 2, 1], ll.to_list())
class Stack:
"""
Stack implementation using linked list which
supports max operation.
Implemented using two linked lists. One for elements
themselfs and one for current max value.
Time complexity: O(1)
Space complexity: O(N) + O(N) for max value.
"""
def __init__(self):
self._main_stack = LinkedList()
self._max_stack = LinkedList()
self._map = {}
def peek(self):
"""
Takes object from the top of this stack
without removing it from the stack.
"""
return self._main_stack.head.value
def pop(self):
"""
Removes object from the top of this stack
and returns that object.
"""
head = self._main_stack.head.value
self._main_stack.delete(0)
self._max_stack.delete(0)
return head
def push(self, item):
"""
Pushes an item onto the top of this stack.
"""
if not self._max_stack.head or self._max_stack.head.value < item:
self._max_stack.prepend(item)
else:
self._max_stack.prepend(self._max_stack.head.value)
self._main_stack.prepend(item)
def max(self):
return self._max_stack.head.value
