Branches - Kelsey

lib/linked_list.rb

@@ -7,39 +7,83 @@ def initialize
     @head = nil
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1), thanks to the power of linked lists we are not making any new data structures, just one new node.
   def add_first(data)
-
+    node = Node.new(data, @head)
+    @head = node
+    return @head.data
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def get_first
-
+    return @head.data if @head
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n), where n is the length of the list
+  # Space complexity - O(1)
   def length
-    return 0
+    count = 0
+    if @head
+      next_node = @head.next
+      count += 1
+      while next_node != nil
+        count += 1
+        next_node = next_node.next
+      end
+    end
+    return count
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def add_last(data)
-
+    if @head
+      if @head.next
+        next_node = @head.next
+        until next_node.next == nil
+          next_node = next_node.next
+        end
+        next_node.next = Node.new(data)
+      else
+        @head.next = Node.new(data)
+      end
+    else
+      @head = Node.new(data)
+    end
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def get_last
-
+    if @head.next
+      last_node = @head.next
+      while last_node.next != nil
+        last_node = last_node.next
+      end
+      return last_node.data
+    elsif @head
+      return @head.data
+    else
+      return nil
+    end
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n), where `n` = index
+  # Space complexity - O(1)
   def get_at_index(index)
-
+    if @head.nil? 
+      return nil
+    else
+      index = index
+      node_index = 0
+      next_node = @head
+      until node_index == index || next_node == nil
+        node_index += 1
+        next_node = next_node.next
+      end
+      return next_node.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