Reversing a Linked List #1

reverser_linked_list_1.rb

class LinkedListNode
  attr_accessor :value, :next_node
 
  def initialize(value, next_node=nil)
    @value = value
    @next_node = next_node
  end
end

def print_values(list_node)
  print "#{list_node.value} --> "
  if list_node.next_node.nil?
    print "nil\n"
    return
  else
    print_values(list_node.next_node)
  end

end
 
class Stack
  attr_reader :data
  
  def initialize
    @data = nil
  end

  def push(value)
    @data = LinkedListNode.new(value, @data)
  end

  def pop
    node = @data.value
    @data = @data.next_node
    return node
  end
end

def reverse_list(list)

  stack = Stack.new

  while list
    stack.push(list.value)
    list = list.next_node
  end

  # return stack.data  
  # this would have worked but it didn't use the 'pop' method, so below includes using pop...

  new_stack = Stack.new
  while stack.data
    new_stack.push(stack.pop)
  end
  stack = new_stack


  reversed_list = nil
  while stack.data
    reversed_list = LinkedListNode.new(stack.pop, reversed_list) 
  end

  return reversed_list
end

node1 = LinkedListNode.new(37)
node2 = LinkedListNode.new(99, node1)
node3 = LinkedListNode.new(12, node2)
 
print_values(node3)

puts "-------"

revlist = reverse_list(node3)

print_values(revlist)