London | 26-SDC-Mar | Ebrahim Beiati-Asl | Sprint 2 | implement_linked_list

Sprint-2/implement_linked_list/linked_list.py

@@ -0,0 +1,47 @@
+class Node:
+    __slots__ = ("value", "previous", "next")
+
+    def __init__(self, value):
+        self.value = value
+        self.previous: "Node | None" = None
+        self.next: "Node | None" = None
+
+
+class LinkedList:
+    def __init__(self):
+        self.head: Node | None = None
+        self.tail: Node | None = None
+
+    def push_head(self, value) -> Node:
+        """Add a value to the front of the list. Returns a handle for O(1) removal."""
+        node = Node(value)
+        if self.head is None:
+            self.head = self.tail = node
+        else:
+            node.next = self.head
+            self.head.previous = node
+            self.head = node
+        return node
+
+    def pop_tail(self):
+        """Remove and return the value at the end of the list."""
+        if self.tail is None:
+            raise IndexError("pop from empty list")
+        node = self.tail
+        self.remove(node)
+        return node.value
+
+    def remove(self, node: Node) -> None:
+        """Remove a node from the list in O(1) using a handle from push_head"""
+        if node.previous is not None:
+            node.previous.next = node.next
+        else:
+            self.head = node.next
+
+        if node.next is not None:
+            node.next.previous = node.previous
+        else:
+            self.tail = node.previous
+
+        node.previous = None
+        node.next = None