completed

lib/linked_list.rb

@@ -7,39 +7,74 @@ def initialize
     @head = nil
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - 0(1)
+  # Space complexity - 0(1)
   def add_first(data)
-
+    @head = Node.new(data, @head)
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - 0(1)
+  # Space complexity - 0(1)
   def get_first
-
+
+      if head
+        return head.data
+      else 
+        return nil
+      end 
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - 0(n)
+  # Space complexity - 0(1)
   def length
-    return 0
+
+    current = head
+    length = 0
+    while current != nil
+      length += 1
+      current = current.next
+    end
+    return length
   end
 
-  # Time complexity - ?
+  # Time complexity - 0(n)
   # Space complexity - ?
   def add_last(data)
 
-  end
+    current = head
+    if current == nil
+      self.add_first(data)
+      return
+    end
+    while current.next != nil
+      current = current.next
+    end
+    current.next = Node.new(data)
+  end	  
 
   # Time complexity - ?
   # Space complexity - ?
   def get_last
+    current = head
+    while current.next != nil
+      current = current.next
+    end
+    return current.data
+  end	  
+
 
-  end
 
   # Time complexity - ?
   # Space complexity - ?
   def get_at_index(index)
+    current = head
+    count = 0
 
+    return nil if current.nil?
+    while count != index
+      count += 1
+      current = current.next
+    end
+    return current.data
   end
-end
+end