Doubly Linked List in Data Structure with Example

A Doubly Linked List is a linked list variant where each node holds references to both the next and previous nodes, allowing traversal in both directions.

Node Structure and Implementation

class Node:
    def __init__(self, data):
        self.data = data
        self.prev = None
        self.next = None

class DoublyLinkedList:
    def __init__(self):
        self.head = None
        self.tail = None

    def append(self, data):
        new_node = Node(data)
        if not self.head:
            self.head = self.tail = new_node
            return
        new_node.prev = self.tail
        self.tail.next = new_node
        self.tail = new_node

    def delete(self, node):
        if node.prev:
            node.prev.next = node.next
        else:
            self.head = node.next
        if node.next:
            node.next.prev = node.prev
        else:
            self.tail = node.prev

Example

Appending 10, 20, 30 to an empty doubly linked list produces: 10 <-> 20 <-> 30, with node 20's prev pointing to 10 and next pointing to 30, allowing traversal from either end.

Complexity

Applications

• Browser forward/backward navigation history.
• Implementing LRU (Least Recently Used) caches.
• Music players with next/previous track functionality.
• Text editors supporting undo/redo in both directions.