Reverse a Singley Linked List

reverse_linked_list.rb

# PROBLEM:
# Given a singley linked list, reverse the list.
#
# SOLUTION:
# Nothing to tricky other to keep track of all the pointers when iterating through.

# Basic object to represent a linked list.
class Node
  attr_accessor :next
  attr_accessor :value

  def initialize(options = {})
    @next = options[:next]
    @value = options[:value]
  end
end

# Simple print method for a linked list
def traverse(root_node)
  current_node = root_node
  while current_node != nil
    puts current_node.value
    current_node = current_node.next 
  end
end

# The reverse implementation
def reverse(root_node)
  previous_node = nil
  current_node = root_node
  while current_node != nil
    next_node = current_node.next
    current_node.next = previous_node
    previous_node = current_node
    current_node = next_node
  end
end

# Build a linked list of A, B, C, D, E
node_e = Node.new(value: "E", next: nil)
node_d = Node.new(value: "D", next: node_e)
node_c = Node.new(value: "C", next: node_d)
node_b = Node.new(value: "B", next: node_c)
node_a = Node.new(value: "A", next: node_b)

traverse(node_a)

reverse(node_a)

traverse(node_e)