[mypy] Fix type annotations for linked_stack.py (TheAlgorithms#5576)

* Fix type annotations for linked_stack.py

* Replace Optional with inline union type

* Rename linked_stack to stack_with_singly_linked_list

* Rename stack_using_dll to stack_with_doubly_linked_list

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: archaengel

DIRECTORY.md

@@ -198,12 +198,12 @@
     * [Evaluate Postfix Notations](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/evaluate_postfix_notations.py)
     * [Infix To Postfix Conversion](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/infix_to_postfix_conversion.py)
     * [Infix To Prefix Conversion](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/infix_to_prefix_conversion.py)
-    * [Linked Stack](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/linked_stack.py)
     * [Next Greater Element](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/next_greater_element.py)
     * [Postfix Evaluation](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/postfix_evaluation.py)
     * [Prefix Evaluation](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/prefix_evaluation.py)
     * [Stack](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/stack.py)
-    * [Stack Using Dll](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/stack_using_dll.py)
+    * [Stack With Doubly Linked List](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/stack_with_doubly_linked_list.py)
+    * [Stack With Singly Linked List](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/stack_with_singly_linked_list.py)
     * [Stock Span Problem](https://github.com/TheAlgorithms/Python/blob/master/data_structures/stacks/stock_span_problem.py)
   * Trie
     * [Trie](https://github.com/TheAlgorithms/Python/blob/master/data_structures/trie/trie.py)

data_structures/stacks/stack_using_dll.py renamed to data_structures/stacks/stack_with_doubly_linked_list.py

@@ -1,19 +1,22 @@
 """ A Stack using a linked list like structure """
 from __future__ import annotations
 
-from typing import Any
+from collections.abc import Iterator
+from typing import Generic, TypeVar
 
+T = TypeVar("T")
 
-class Node:
-    def __init__(self, data):
+
+class Node(Generic[T]):
+    def __init__(self, data: T):
         self.data = data
-        self.next = None
+        self.next: Node[T] | None = None
 
-    def __str__(self):
+    def __str__(self) -> str:
         return f"{self.data}"
 
 
-class LinkedStack:
+class LinkedStack(Generic[T]):
     """
     Linked List Stack implementing push (to top),
     pop (from top) and is_empty
@@ -44,15 +47,15 @@ class LinkedStack:
     """
 
     def __init__(self) -> None:
-        self.top: Node | None = None
+        self.top: Node[T] | None = None
 
-    def __iter__(self):
+    def __iter__(self) -> Iterator[T]:
         node = self.top
         while node:
             yield node.data
             node = node.next
 
-    def __str__(self):
+    def __str__(self) -> str:
         """
         >>> stack = LinkedStack()
         >>> stack.push("c")
@@ -63,7 +66,7 @@ def __str__(self):
         """
         return "->".join([str(item) for item in self])
 
-    def __len__(self):
+    def __len__(self) -> int:
         """
         >>> stack = LinkedStack()
         >>> len(stack) == 0
@@ -87,7 +90,7 @@ def is_empty(self) -> bool:
         """
         return self.top is None
 
-    def push(self, item: Any) -> None:
+    def push(self, item: T) -> None:
         """
         >>> stack = LinkedStack()
         >>> stack.push("Python")
@@ -101,7 +104,7 @@ def push(self, item: Any) -> None:
             node.next = self.top
         self.top = node
 
-    def pop(self) -> Any:
+    def pop(self) -> T:
         """
         >>> stack = LinkedStack()
         >>> stack.pop()
@@ -125,7 +128,7 @@ def pop(self) -> Any:
         self.top = self.top.next
         return pop_node.data
 
-    def peek(self) -> Any:
+    def peek(self) -> T:
         """
         >>> stack = LinkedStack()
         >>> stack.push("Java")