Branches, Kristy

lib/linked_list.rb

@@ -7,39 +7,71 @@ 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
-
+    return nil if head.nil?
+    return @head.data if !head.nil?
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(n)
   def length
-    return 0
+    if @head.nil?
+      return 0
+    end
+    current = @head
+    length = 1
+    until current.next.nil?
+      length += 1
+      current = current.next
+    end
+    return length
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(n)
   def add_last(data)
-
+    if @head.nil?
+      @head = Node.new(data)
+    else
+      last = self.find_last
+      last.next = Node.new(data)
+    end
+
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
-  def get_last
+  def find_last
+    current = @head
+    until current.next.nil?
+      current = current.next
+    end
+    return current
+  end
 
+  # Time complexity - O(n)
+  # Space complexity - O(n)
+  def get_last  
+    return self.find_last.data
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(n)
   def get_at_index(index)
-
+    current = @head
+    index.times do
+      if current.nil? || current.next.nil?
+        return nil
+      else
+        current = current.next
+      end
+    end
+    return current.data
   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