Implemented methods

lib/linked_list.rb

@@ -2,44 +2,80 @@
 
 class LinkedList
   attr_reader :head
-
+  
   def initialize
     @head = nil
   end
-
-  # Time complexity - ?
-  # Space complexity - ?
+  
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def add_first(data)
-
-  end
-
-  # Time complexity - ?
-  # Space complexity - ?
+    current = head
+    @head = Node.new(data, current)
+  end 
+
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def get_first
-
+    return nil if head.nil?
+    return head.data
   end
-
-  # Time complexity - ?
-  # Space complexity - ?
+  
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def length
-    return 0
+    node = head
+    count = 0
+
+    return 0 if head == nil
+
+    until node == nil
+      count += 1
+      node = node.next
+    end
+    return count
   end
-
-  # Time complexity - ?
-  # Space complexity - ?
+  
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def add_last(data)
-
+    if head.nil?
+      @head = Node.new(data)
+      return head.data
+    end
+
+    current = head
+    until current.next == nil
+      current = current.next
+    end
+
+    node = Node.new(data)
+    current.next = node
+    return node.data
   end
-
-  # Time complexity - ?
-  # Space complexity - ?
+  
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def get_last
-
+    current = head
+
+    until current.next == nil
+      current = current.next
+    end
+
+    return current.data
   end
-
-  # Time complexity - ?
-  # Space complexity - ?
+  
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def get_at_index(index)
-
+    return nil if head == nil
+    current = head
+    index.times do 
+      current = current.next
+    end
+
+    return current.data
   end
+
 end

test/linked_list_test.rb

@@ -12,50 +12,50 @@
   before do
     @list = LinkedList.new
   end
-
+  
   describe 'initialize' do
     it 'can be created' do
-
+      
       # Assert
       expect(@list).must_be_kind_of LinkedList
     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)
-
-        # Assert
-        expect(@list.get_first).must_equal 3
+      @list.add_first(3)
+      
+      # Assert
+      expect(@list.get_first).must_equal 3
     end
-
+    
     it 'will put the last added item to the front of the list' do
       # Act
       @list.add_first(1)
       @list.add_first(2)
-
+      
       # Assert
       expect(@list.get_first).must_equal 2
-
+      
       # Act again
       @list.add_first(3)
-
+      
       # Assert
       expect(@list.get_first).must_equal 3
     end
-
+    
     it 'will return `nil` for `getFirst` if the list is empty' do
-
+      
       expect(@list.get_first).must_be_nil
     end
   end
-
-  xdescribe "length" do
+  
+  describe "length" do
     it "will return 0 for an empty list" do
       expect(@list.length).must_equal 0
     end
-
+    
     it "will return the length for nonempty lists" do
       count = 0
       while count < 5
@@ -65,43 +65,43 @@
       end
     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
     end
-
+    
     it "will put new items to the rear of the list" do
       @list.add_last(2)
       expect(@list.length).must_equal 1
       expect(@list.get_last).must_equal 2
-
+      
       @list.add_last(3)
       expect(@list.get_first).must_equal 2
       expect(@list.get_last).must_equal 3
       expect(@list.length).must_equal 2
-
+      
       @list.add_last(4)
       expect(@list.get_first).must_equal 2
       expect(@list.get_last).must_equal 4
       expect(@list.length).must_equal 3
-
+      
     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
-
+    
     it 'can retrieve an item at an index in the list' do
       @list.add_first(1)
       @list.add_first(2)
       @list.add_first(3)
       @list.add_first(4)
-
+      
       expect(@list.get_at_index(0)).must_equal 4
       expect(@list.get_at_index(1)).must_equal 3
       expect(@list.get_at_index(2)).must_equal 2