require_relative 'singly_linked_list'

class LinkedStack < LinkedList
  def empty?
    @length == 0
  end

  def push(data)
    new_head      = Node.new(data)
    new_head.next = @head
    @length      += 1
    @head         = new_head
  end

  def pop
    return nil if empty?
    data     = @head.data
    @head    = @head.next
    @length -= 1
    data
  end

  def peek
    self[0]
  end
end