Earth - Emily

lib/linked_list.rb

@@ -1,45 +1,83 @@
 require_relative 'node'
 
 class LinkedList
-  attr_reader :head
+  attr_reader :head, :tail
 
   def initialize
     @head = nil
+    @tail = tail
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def add_first(data)
+    first = Node.new(data)
 
+    if @head
+      first.next = @head
+    end
+
+    @head = first
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def get_first
+    if @head.nil?
+      return nil
+    end
+
+    return @head.data
 
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def length
-    return 0
+    count = 0
+    current = @head
+
+    while current != nil
+      count += 1
+      current = current.next
+    end
+
+    return count
+
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def add_last(data)
+   last = Node.new(data)
 
+  @tail ? @tail.next = last : @head = last
+   @tail = last
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def get_last
+    if @tail.nil?
+      return nil
+    end
 
+    return @tail.data
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(n)
   def get_at_index(index)
+    return @head.data if index.zero?
+    current_index = 0
+    current = @head
+
+    until current.nil?
+      current = current.next
+      current_index += 1
 
+      return current.data if current_index == index
+    end
+    return nil
   end
 end

test/linked_list_test.rb

@@ -21,7 +21,7 @@
     end
   end
 
-  xdescribe 'add_first & get_first' do
+  describe 'add_first & get_first' do
     it 'can add values to an empty list' do
       # Act
         @list.add_first(3)
@@ -51,7 +51,7 @@
     end
   end
 
-  xdescribe "length" do
+  describe "length" do
     it "will return 0 for an empty list" do
       expect(@list.length).must_equal 0
     end
@@ -66,7 +66,7 @@
     end
   end
 
-  xdescribe "addLast & getLast" do
+  describe "addLast & getLast" do
     it "will add to the front if the list is empty" do
       @list.add_last(1)
       expect(@list.get_first).must_equal 1
@@ -93,7 +93,7 @@
     end
   end
 
-  xdescribe 'get_at_index' do
+  describe 'get_at_index' do
     it 'returns nil if the index is outside the bounds of the list' do
       expect(@list.get_at_index(3)).must_be_nil
     end