Python/data_structures/stacks/linked_stack.py

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""" A Stack using a linked list like structure """
from typing import Any, Optional
class Node:
def __init__(self, data):
self.data = data
self.next = None
def __str__(self):
return f"{self.data}"
class LinkedStack:
"""
Linked List Stack implementing push (to top),
pop (from top) and is_empty
>>> stack = LinkedStack()
>>> stack.is_empty()
True
>>> stack.push(5)
>>> stack.push(9)
>>> stack.push('python')
>>> stack.is_empty()
False
>>> stack.pop()
'python'
>>> stack.push('algorithms')
>>> stack.pop()
'algorithms'
>>> stack.pop()
9
>>> stack.pop()
5
>>> stack.is_empty()
True
>>> stack.pop()
Traceback (most recent call last):
...
IndexError: pop from empty stack
"""
def __init__(self) -> None:
self.top: Optional[Node] = None
def __iter__(self):
node = self.top
while node:
yield node.data
node = node.next
def __str__(self):
"""
>>> stack = LinkedStack()
>>> stack.push("c")
>>> stack.push("b")
>>> stack.push("a")
>>> str(stack)
'a->b->c'
"""
return "->".join([str(item) for item in self])
def __len__(self):
"""
>>> stack = LinkedStack()
>>> len(stack) == 0
True
>>> stack.push("c")
>>> stack.push("b")
>>> stack.push("a")
>>> len(stack) == 3
True
"""
return len(tuple(iter(self)))
def is_empty(self) -> bool:
"""
>>> stack = LinkedStack()
>>> stack.is_empty()
True
>>> stack.push(1)
>>> stack.is_empty()
False
"""
return self.top is None
def push(self, item: Any) -> None:
"""
>>> stack = LinkedStack()
>>> stack.push("Python")
>>> stack.push("Java")
>>> stack.push("C")
>>> str(stack)
'C->Java->Python'
"""
node = Node(item)
if not self.is_empty():
node.next = self.top
self.top = node
def pop(self) -> Any:
"""
>>> stack = LinkedStack()
>>> stack.pop()
Traceback (most recent call last):
...
IndexError: pop from empty stack
>>> stack.push("c")
>>> stack.push("b")
>>> stack.push("a")
>>> stack.pop() == 'a'
True
>>> stack.pop() == 'b'
True
>>> stack.pop() == 'c'
True
"""
if self.is_empty():
raise IndexError("pop from empty stack")
assert isinstance(self.top, Node)
pop_node = self.top
self.top = self.top.next
return pop_node.data
def peek(self) -> Any:
"""
>>> stack = LinkedStack()
>>> stack.push("Java")
>>> stack.push("C")
>>> stack.push("Python")
>>> stack.peek()
'Python'
"""
if self.is_empty():
raise IndexError("peek from empty stack")
assert self.top is not None
return self.top.data
def clear(self) -> None:
"""
>>> stack = LinkedStack()
>>> stack.push("Java")
>>> stack.push("C")
>>> stack.push("Python")
>>> str(stack)
'Python->C->Java'
>>> stack.clear()
>>> len(stack) == 0
True
"""
self.top = None
if __name__ == "__main__":
from doctest import testmod
testmod()