palindrome_linked_list.rb

# Refactor/rewrite this file

class Node
  attr_accessor :value, :next

  def initialize(val, next_in_line)
    @value = val
    @next  = next_in_line
  end
end

class LinkedList
  attr_accessor :head

  def initialize(val)
    @head = Node.new(val, nil)
  end

  def add(value)
    # Traverse to the end of the list
    # And insert a new node over there with the specified value
    current      = @head
    current      = current.next until current.next.nil?
    current.next = Node.new(value, nil)
    self
  end

  def delete(val)
    current = @head
    if current.value == val
        @head = @head.next
    else
      until current.next.nil?
        current = current.next
        if current.value == val
          current.value = current.next.value || nil
          current.next  = current.next.next
        end
      end
    end
    @head
  end
end

def list_palindrome(list)
  stack   = []
  current = list.head

  while current
    stack.push(current.value)
    current = current.next
  end

  current = list.head

  while current
    stack_temp = stack.pop
    return false unless current.value == stack_temp
    current = current.next
  end
  true
end

def list_check(list)
  return false unless list

  stack = []
  slow  = fast = list.head

  while fast && !fast.next.nil?
    fast = fast.next.next
    stack.push(slow.value)
    slow = slow.next
  end

  slow = slow.next unless fast.nil?

  until slow.nil?
    temp = stack.pop
    return false unless slow.value == temp
    slow = slow.next
  end

  true
end