diff --git a/DIRECTORY.md b/DIRECTORY.md
index 6fbd5e2cc1c5..88df541eaf6a 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -126,6 +126,7 @@
   * [Molecular Chemistry](https://github.com/TheAlgorithms/Python/blob/master/conversions/molecular_chemistry.py)
   * [Octal To Decimal](https://github.com/TheAlgorithms/Python/blob/master/conversions/octal_to_decimal.py)
   * [Prefix Conversions](https://github.com/TheAlgorithms/Python/blob/master/conversions/prefix_conversions.py)
+  * [Pressure Conversions](https://github.com/TheAlgorithms/Python/blob/master/conversions/pressure_conversions.py)
   * [Rgb Hsv Conversion](https://github.com/TheAlgorithms/Python/blob/master/conversions/rgb_hsv_conversion.py)
   * [Roman Numerals](https://github.com/TheAlgorithms/Python/blob/master/conversions/roman_numerals.py)
   * [Temperature Conversions](https://github.com/TheAlgorithms/Python/blob/master/conversions/temperature_conversions.py)
@@ -196,12 +197,12 @@
     * [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)
@@ -858,6 +859,8 @@
     * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_301/sol1.py)
   * Problem 551
     * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_551/sol1.py)
+  * Problem 686
+    * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_686/sol1.py)
 
 ## Quantum
   * [Deutsch Jozsa](https://github.com/TheAlgorithms/Python/blob/master/quantum/deutsch_jozsa.py)
diff --git a/data_structures/stacks/stack_using_dll.py b/data_structures/stacks/stack_with_doubly_linked_list.py
similarity index 100%
rename from data_structures/stacks/stack_using_dll.py
rename to data_structures/stacks/stack_with_doubly_linked_list.py
diff --git a/data_structures/stacks/linked_stack.py b/data_structures/stacks/stack_with_singly_linked_list.py
similarity index 83%
rename from data_structures/stacks/linked_stack.py
rename to data_structures/stacks/stack_with_singly_linked_list.py
index 85b59a940e39..903ae39db4b5 100644
--- a/data_structures/stacks/linked_stack.py
+++ b/data_structures/stacks/stack_with_singly_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")