Built Stack functionality + Cleaned Up DoublyLinkedList.py

Author: pythonioncoder

DoublyLinkedList.py

@@ -123,16 +123,3 @@ def remove(self, index):
 			self.length -= 1
 			return temp
 		return None
-
-
-dll = DoublyLinkedList(0)
-dll.append(1)
-dll.append(2)
-dll.append(3)
-dll.append(4)
-dll.append(5)
-dll.append(6)
-dll.append(7)
-dll.append(8)
-dll.append(9)
-dll.print_list()

Stack.py

@@ -0,0 +1,59 @@
+'''
+Overview:
+Stacks are like a stack of books.
+Add an item onto the stack - Push
+You can only reach the last item pushed
+Removing last added item - Pop
+LIFO - Last In First Out
+
+Benefits:
+	O(1) to Push/Pop
+
+Examples:
+	Browser History (Back Button)
+	Recursion
+
+Implementation:
+	List
+	Linked List
+	Stack should point down so popping/pushing the top value is O(1)
+		without needing to find the second last node
+'''
+
+
+class Node:
+	def __init__(self, value):
+		self.value = value
+		self.next = None
+
+
+class Stack:
+	def __init__(self, value):
+		new_node = Node(value)
+		self.top = new_node
+		self.height = 1
+
+	def print_stack(self):
+		temp = self.top
+		while temp is not None:
+			print(temp.value)
+			temp = temp.next
+
+	def push(self, value):
+		# O(1)
+		new_node = Node(value)
+		if self.top is None:
+			self.top = new_node
+		else:
+			new_node.next = self.top
+			self.top = new_node
+		self.height += 1
+
+	def pop(self):
+		if self.top is None:
+			return None
+		temp = self.top
+		self.top = self.top.next
+		temp.next = None
+		self.height -= 1
+		return temp