Branches, C. Gutierrez

lib/double_linked_list.rb

@@ -0,0 +1,195 @@
+# Defines a node in the double linked list
+class Node
+  attr_reader :data
+  attr_accessor :next
+  attr_accessor :prev
+
+  def initialize(value, next_node = nil, previous_node = nil)
+    @data = value
+    @next = next_node
+    @prev = previous_node
+  end
+end
+
+class DoubleLinkedList
+
+  def initialize
+    @head = nil
+  end 
+
+  def add_first(value)
+    current = @head
+    temp = Node.new(value)
+    if current == nil
+      @head = temp
+    else
+      temp.next = current
+      current.prev = temp
+      @head = temp
+    end
+  end
+
+  def get_first
+    current = @head
+    if current == nil
+      return nil
+    else
+      return current.data
+    end
+  end
+
+  def length
+    current = @head
+    if current == nil
+      return 0
+    end
+
+    length = 1
+
+    until current.next == nil do
+      current = current.next
+      length += 1  
+    end
+
+    return length 
+
+  end
+
+  def add_last(value)
+    # create a new node
+    temp = Node.new(value) 
+
+    # set current
+    current = @head
+
+    # shortcut for an empty list
+    if current == nil
+      add_first(value)
+      return
+    elsif current.next == nil
+      current.next = temp
+      temp.prev = current
+      return
+    end
+
+    # increment current to pentultimate node
+    until current.next == nil do
+      current = current.next
+    end
+
+    current.next = temp
+    temp.prev = current
+
+  end
+
+  def get_last
+    current = @head
+
+    if current == nil
+      return nil
+    end
+
+    until current.next == nil do
+      current = current.next
+    end
+
+    return current.data
+  end
+
+  def get_at_index(index)
+    current = @head
+
+    if current == nil 
+      return nil
+    elsif index == 0
+      return current.data
+    end
+
+    counter = 0
+
+    until current.next == nil do
+      if counter == index
+        return current.data
+      else
+        current = current.next
+        counter += 1
+      end
+    end
+
+    if index > counter 
+      return nil
+    else
+      return current.data
+    end
+
+  end
+
+  def find_nth_from_end(index) 
+    current = @head
+
+    if current == nil
+      return nil
+    end
+
+    length = 0
+    # get current to the end
+    until current.next == nil do
+      current = current.next
+      length += 1
+    end
+
+    # see if the index value is longer than the list
+    if index > length
+      return nil
+    elsif index == 0
+      return current.data
+    end
+
+    #hop back
+    counter = 0
+    until counter == index do
+      current = current.prev
+      counter += 1
+    end
+
+    return current.data
+  end
+
+  def reverse
+    current = @head
+
+    if current == nil || current.next == nil
+      return
+    end
+
+    hopper = @head
+
+    until hopper.next == nil do
+      hopper = hopper.next
+    end
+
+    @head = current
+
+    return
+
+  end
+
+  def delete(value)
+  end
+
+  def view
+    current = @head
+
+    if current == nil
+      return
+    end
+
+    until current.next == nil
+      puts current.data
+      current = current.next
+    end
+    puts current.data
+
+  end
+
+end