doubly_linked_list.rb

# frozen_string_literal: true

# Class to represent each node from the linked list
class Node
  attr_accessor :data, :next, :previous

  def initialize(data)
    @data = data
    @next = nil
    @previous = nil
  end
end

# Implement a doubly linked list
class DoublyLinkedList
  def initialize
    @head = nil
  end

  def append(data)
    if @head.nil?
      @head = Node.new(data)
    else
      tail_node = find_tail
      new_node = Node.new(data)
      tail_node.next = new_node
      new_node.previous = tail_node
    end
  end

  def find_tail
    current_tail = @head
    current_tail = current_tail.next until current_tail.next.nil?
    current_tail
  end

  def delete(value)
    if @head.data == value
      @head = @head.next
      @head.previous = nil
    else
      target = find(value)
      if target.next.nil?
        target.previous.next = nil
      else
        target.previous.next = target.next
        target.next.previous = target.previous
      end
    end
  end

  def find(value)
    current = @head
    current = current.next until current.data == value
    current
  end

  def insert_after(target, value)
    current = find(target)
    temp = current.next
    current.next = Node.new(value)
    current.next.next = temp
    current.next.previous = current
    current.next.next.previous = current.next
  end

  def print_list
    current = @head
    puts "List: "
    until current.nil?
      print "#{current.data} "
      current = current.next
    end
  end
end

list = DoublyLinkedList.new
list.append(10)
list.append(20)
list.append(30)
list.insert_after(20, 22)
list.print_list
list.delete(30)
list.print_list
list.delete(10)
list.print_list