class LinkedList
	def initialize()
		@head = nil
		@tail = nil
		@totalNodes = 0
	end

	def atIndex (index) 
		tmp = @head
		k = 0
		while tmp and k<index
			tmp = tmp.next
			k+=1
		end
		if tmp != nil
			return tmp.data
		else
			return nil
		end
	end

	def insert(obj, index)
		if self.empty?
			@head = obj
			@tail = obj
			@totalNodes += 1
		end

		tmp = self.atIndex(index)
		if tmp == nil
			return nil
		elsif tmp.doubleAttached?
			tmp.previous.next = obj
			obj.previous = tmp.previous
			obj.next = tmp
			tmp.previous = obj
			tmp = nil
		elsif tmp.frontlyAttached?
			tmp.next = obj
			obj.previous = tmp
		elsif tmp.rearlyAttached?
			tmp.previous = obj
			obj.next = tmp
		end
		return obj
	end

	def removeObject(index)
		tmp = self.atIndex(index)
		if tmp == nil
			return nil
		end
		if tmp.doublyAttached?
			tmp.previous.next = tmp.next
			tmp.next.previous = tmp.previous
			tmp.next = nil
			tmp.previous = nil
		end
		if tmp.frontlyAttached?
			tmp.previous.next = nil
			tmp.previous = nil
		end
		if tmp.rearlyAttached?
			tmp.next.previous = nil
			tmp.next = nil
		end
		return self
	end

	def empty? 
		if @totalnodes == 0
			true
		else
			false
		end
	end
end

class Node
	def initialize()
		@data = nil
		@next = nil
		@previous = nil
	end

	def data=(obj)
		@data = obj
	end

	def data
		@data
	end

	def next=(obj)
		@next = obj
	end

	def next
		@next
	end

	def previous
		@previous
	end

	def previous=(obj)
		@previous = obj
	end

	def attached?
		if self.frontlyAttached? || self.rearlyAttached? do
			return true
		else
			return false
		end
	end

	def doublyAttached?
		if self.frontlyAttached? && self.rearlyAttached? do
			return true
		else
			return false
		end
	end

	def frontlyAttached?
		if @previous != nil do
			return true
		else
			return false
		end
	end

	def rearlyAttached?
		if @next != nil do
			return true
		else
			return false
		end
	end
end