LinkedList implementation with double linked list.

Author: Emilianouz

Sprint-2/implement_linked_list/linked_list.py

@@ -0,0 +1,59 @@
+# `push_head` should add an element to the start of the list. It should return something that can be passed to 
+# `remove` to remove that element in the future.
+# `pop_tail` should remove an element from the end of the list.
+# `remove` takes a handle from `push_head`, and removes that element from the list.
+
+class LinkedList:
+    class _Node:  # to have O(1) must be implemented double linked list to access previous
+        __slots__ = ("value", "prev", "next")
+
+        def __init__(self, value):
+            self.value = value
+            self.prev = None
+            self.next = None
+
+    def __init__(self):
+        self.head = None
+        self.tail = None
+
+    def push_head(self, value):
+        node = self._Node(value)
+
+        node.next = self.head
+        if self.head:
+            self.head.prev = node
+        else:
+            # when list gets empty, tail also becomes this node
+            self.tail = node
+
+        self.head = node
+        return node  # handling
+
+    def pop_tail(self):
+        if not self.tail:
+            raise IndexError("pop from empty list")
+
+        node = self.tail
+        value = node.value
+
+        self.tail = node.prev
+        if self.tail:
+            self.tail.next = None
+        else:
+            # when the list gets empty
+            self.head = None
+
+        return value
+
+    def remove(self, node):
+        if node.prev:
+            node.prev.next = node.next
+        else:
+            # removes head
+            self.head = node.next
+
+        if node.next:
+            node.next.prev = node.prev
+        else:
+            # removes tail
+            self.tail = node.prev