Branches - Dora

lib/linked_list.rb

@@ -7,39 +7,76 @@ def initialize
     @head = nil
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   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
-
+    if head.nil?
+      return nil
+    else
+      return head.data
+    end
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def length
-    return 0
+    count = 0
+    current = head
+    until current.nil?
+      current = current.next
+      count += 1
+    end
+
+    return count
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def add_last(data)
-
+    current = head
+    if current.nil?
+      @head = Node.new(data, @head)
+    else
+      until current.next.nil?
+        current = current.next
+      end
+      current.next = Node.new(data, nil)
+    end
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def get_last
-
+    current = head
+    if current.nil?
+      return nil
+    else
+      until current.next.nil?
+        current = current.next
+      end
+      return current.data
+    end
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def get_at_index(index)
-
+    current = head
+    if current.nil?
+      return nil
+    elsif index == 0
+      return current.data
+    else
+      index.times do
+        current = current.next
+      end
+      return current.data
+    end
   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