London|25-SDC-November| Donara Blanc |Sprint 2 |Linked_list

Sprint-2/implement_linked_list/linked_list.py

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+class Node:
+    def __init__(self, value):
+        self.value = value
+        self.next = None
+        self.previous = None
+
+
+class LinkedList:
+    def __init__(self):
+        self.head = None
+        self.tail = None
+
+    def push_head(self, value):
+        """Insert a new node at the head and return the node."""
+        new_node = Node(value)
+
+        if self.head is None:
+            # Empty list: head and tail are the same node
+            self.head = new_node
+            self.tail = new_node
+        else:
+            # Non‑empty: link new node before current head
+            new_node.next = self.head
+            self.head.previous = new_node
+            self.head = new_node
+
+        return new_node
+
+    def pop_tail(self):
+        """Remove the tail node and return its value."""
+        if self.tail is None:
+            raise IndexError("pop from empty linked list")
+
+        node = self.tail
+        value = node.value
+
+        # Move tail backwards
+        self.tail = node.previous
+
+        if self.tail is None:
+            # List is now empty
+            self.head = None
+        else:
+            self.tail.next = None
+
+        # Fully detach the old node (good hygiene)
+        node.next = None
+        node.previous = None
+
+        return value
+
+    def remove(self, node):
+        """Remove an arbitrary node from the list."""
+        if node is None:
+            return
+
+        # Fix previous node's next pointer
+        if node.previous is not None:
+            node.previous.next = node.next
+        else:
+            # node was head
+            self.head = node.next
+
+        # Fix next node's previous pointer
+        if node.next is not None:
+            node.next.previous = node.previous
+        else:
+            # node was tail
+            self.tail = node.previous
+
+        # Detach removed node
+        node.next = None
+        node.previous = None