Reverse a linked list by implementing a stack data structure.

linked_list_stack.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

  # Push a value onto the stack
  def push(value)
    @data = LinkedListNode.new(value, @data)
  end

  # Pop an item off the stack.  
  # Remove the last item that was pushed onto the
  # stack and return the value to the user
  def pop
    if @data.nil?
      puts "Underflow"
    else
      @data = @data.next_node
    end
  end
end

def reverse_list(list)
  stack = Stack.new 
  
  while list 
    stack.push(list.value)
    list = list.next_node
  end

  return stack.data
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)