Add Ruby snippet for implementing a doubly linked list with node insertion and traversal

Author: ACR1209

snippets/ruby/data-structures/doubly-linked-list.md

@@ -0,0 +1,75 @@
+---
+title: Doubly Linked List
+description: Implements a doubly linked list with node insertion and traversal.
+author: ACR1209
+tags: ruby,data structures,linked list,doubly linked list
+---
+
+```rb
+class Node
+  attr_accessor :data, :next, :prev
+
+  def initialize(data)
+    @data = data
+    @next = nil
+    @prev = nil
+  end
+end
+
+class DoublyLinkedList
+  def initialize
+    @head = nil
+    @tail = nil
+  end
+
+  def append(data)
+    new_node = Node.new(data)
+    if @head.nil?
+      @head = new_node
+      @tail = new_node
+    else
+      @tail.next = new_node
+      new_node.prev = @tail
+      @tail = new_node
+    end
+  end
+
+  def prepend(data)
+    new_node = Node.new(data)
+    if @head.nil?
+      @head = new_node
+      @tail = new_node
+    else
+      new_node.next = @head
+      @head.prev = new_node
+      @head = new_node
+    end
+  end
+
+  def display_forward
+    current = @head
+    while current
+      print "#{current.data} <-> "
+      current = current.next
+    end
+    puts "nil"
+  end
+
+  def display_backward
+    current = @tail
+    while current
+      print "#{current.data} <-> "
+      current = current.prev
+    end
+    puts "nil"
+  end
+end
+
+# Usage:
+dll = DoublyLinkedList.new
+dll.append(1)
+dll.append(2)
+dll.append(3)
+dll.display_forward # Output: 1 <-> 2 <-> 3 <-> nil
+dll.display_backward # Output: 3 <-> 2 <-> 1 <-> nil
+```