Linked List Challenge

linked_list_challenge.rb

class LinkedList
  attr_reader :head
  attr_accessor :tail

  def self.from_ruby_list(list)
    return nil if list.empty?
    new(list[0], self.from_ruby_list(list[1..]))
  end

  def initialize(head, tail = nil)
    validate_tail!(tail)
    @head = head
    @tail = tail
  end

  def inspect
    "{#{head} -> #{tail.inspect}}"
  end

  private

  def validate_tail!(tail)
    return if tail.is_a? LinkedList
    return if tail.nil?
    fail "Tail must be a LinkedList or nil, given #{tail.class}."
  end
end

# Want more info on linked lists?
# Try here: https://www.rubyguides.com/2017/08/ruby-linked-list/

puts "== Trying out some features =="
list = LinkedList.new('a', LinkedList.new('b', nil))
p list
# {a -> {b -> nil}}
p list.head
# => "a"
p list.tail
# => {b -> nil}
p list.tail.head
# => "b"
p list.tail.tail
# => nil

puts
puts "== Changing the tail =="
list.tail = LinkedList.new('bat', LinkedList.new('rat', nil))
p list
# => {a -> {bat -> {rat -> nil}}}

puts
puts "== Trying a longer one =="
puts LinkedList.from_ruby_list([1, 2, 3, 4, 5]).inspect
# => {1 -> {2 -> {3 -> {4 -> {5 -> nil}}}}}

def reverse(list, new_tail = nil)
  # The challenge is to reverse the given `list` without initialising any
  # new LinkedLists or amending the LinkedList class. Note that you _can_
  # change the tail for each item.
end

puts
puts "== Reversing! =="
puts reverse(LinkedList.from_ruby_list([1, 2, 3, 4, 5])).inspect
# => {5 -> {4 -> {3 -> {2 -> {1 -> nil}}}}}