Branches - Mira

lib/linked_list.rb

@@ -7,39 +7,44 @@ def initialize
     @head = nil
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(n)
   def add_first(data)
-
+    @head = Node.new(data, @head)
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def get_first
-
+    @head&.data
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
-  def length
-    return 0
+  # Time complexity - O(n)
+  # Space complexity - O(n)
+  def length(node=@head, len=0)
+    return len unless node
+    return length(node.next, len.succ)
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
-  def add_last(data)
-
+  # Time complexity - O(n)
+  # Space complexity - O(n)
+  def add_last(data, node=@head)
+    return add_first(data) unless node
+    return node.next = Node.new(data) unless node.next
+    return add_last(data, node.next)
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
-  def get_last
-
+  # Time complexity - O(n)
+  # Space complexity - O(n)
+  def get_last(node=@head)
+    return node&.data unless node&.next
+    return get_last(node.next)
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
-  def get_at_index(index)
-
+  # Time complexity - O(index)
+  # Space complexity - O(index)
+  def get_at_index(index, node=@head)
+    return node&.data unless node&.next && index > 0
+    return get_at_index(index.pred, node.next)
   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
@@ -91,7 +91,7 @@
 
   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