diff --git a/lib/fibonacci.rb b/lib/fibonacci.rb
index 7465c25..23e3b18 100644
--- a/lib/fibonacci.rb
+++ b/lib/fibonacci.rb
@@ -1,8 +1,26 @@
 # Improved Fibonacci
 
-# Time Complexity - ?
-# Space Complexity - ?  (should be O(n))
-# Hint, you may want a recursive helper method
+# Time Complexity - O(n)
+# Space Complexity - O(n)
 def fibonacci(n)
- 
+  raise ArgumentError.new "n must be greater than or equal to 0" if n < 0
+  
+  fib_array = [0, 1]
+  while fib_array.length < n + 1
+    fib_array.push(0)
+  end
+  
+  if n <= 1
+    return n 
+  else
+    if fib_array[n - 1] == 0
+      fib_array[n - 1] = fibonacci(n - 1)
+    end
+    if fib_array[n - 2] == 0
+      fib_array[n - 2] = fibonacci(n - 2)
+    end
+  end
+  
+  fib_array[n] = fib_array[n - 2] + fib_array[n - 1]
+  return fib_array[n]
 end
diff --git a/lib/super_digit.rb b/lib/super_digit.rb
index 33e367f..cf984a6 100644
--- a/lib/super_digit.rb
+++ b/lib/super_digit.rb
@@ -1,15 +1,22 @@
 # Superdigit
 
-# Time Complexity - ?
-# Space Complexity - ?
+# Time Complexity - O(n)
+# Space Complexity - O(n)
 def super_digit(n)
-   
-end
+  return n if n < 10
   
+  sum = 0
+  while n > 0
+    sum += n % 10
+    n /= 10
+  end
+
+  return super_digit(sum)
+end
+
 
-# Time Complexity - ?
-# Space Complexity - ?
+# Time Complexity - Is this O(2^n) (exponential), because the method gets called twice each time?
+# Space Complexity - Is this O(2^n) (exponential), because the method gets called twice each time?
 def refined_super_digit(n, k)
-    
+  return super_digit(super_digit(n) * k)
 end
-    
\ No newline at end of file
diff --git a/test/super_digit_test.rb b/test/super_digit_test.rb
index 60da3a1..8eb6475 100644
--- a/test/super_digit_test.rb
+++ b/test/super_digit_test.rb
@@ -1,6 +1,6 @@
 require_relative "test_helper"
 
-xdescribe "super_digit" do
+describe "super_digit" do
   it "will return 2 for super_digit(9875)" do
     # Act
     answer = super_digit(9875)