Janice H.

lib/fibonacci.rb

@@ -1,8 +1,19 @@
-# Improved Fibonacci
+# # Improved Fibonacci
+
+# # Time Complexity - O(n)
+# # Space Complexity - O(n)  (should be O(n))
+# # Hint, you may want a recursive helper method
 
-# Time Complexity - ?
-# Space Complexity - ?  (should be O(n))
-# Hint, you may want a recursive helper method
 def fibonacci(n)
-
+  raise ArgumentError if n < 0
+  return fib_helper([0, 1], 2, n)
+end
+
+def fib_helper(fib_saver, current, n)
+  return n if n == 0 || n == 1
+  return fib_saver.sum if current == n
+  new_sum = fib_saver.sum
+  fib_saver[0] = fib_saver[1]
+  fib_saver[1] = new_sum
+  return fib_helper(fib_saver, current + 1, n)
 end

lib/super_digit.rb

@@ -1,15 +1,23 @@
 # Superdigit
 
-# Time Complexity - ?
-# Space Complexity - ?
+# Time Complexity - O(nlog10n)?
+# Space Complexity - O(log10n)?
 def super_digit(n)
-
+  return n if n < 10
+  super_digit(digitize(n))
 end
-
 
-# Time Complexity - ?
-# Space Complexity - ?
+def digitize(n)
+  return n if n < 10
+  sum = 0
+  single_digit = n % 10
+  sum += single_digit
+  return sum + digitize(n / 10)
+end
+
+
+# Time Complexity - I'm pretty sure this solution doesn't reduce the time complexity, unfortunately. So it's O(nlog10n) still?
+# Space Complexity - O(log10n)?
 def refined_super_digit(n, k)
-    
+  super_digit(n * k)
 end
-

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)
@@ -33,13 +33,13 @@
     expect(answer).must_equal 6
   end
 
-  describe "refined superdigit" do 
+  describe "refined superdigit" do
     it "will return 1 for n = 1 and k = 1" do
       # Act
       answer = refined_super_digit(1, 1)
 
       # Assert
-      expect(answer).must_equal 1      
+      expect(answer).must_equal 1
     end
 
     it "will return 8 for n=9875 and k = 4" do
@@ -53,7 +53,7 @@
     it "will return 3 for n=148 and k = 3" do
         # Act
         answer = refined_super_digit(148, 3)
-  
+
         # Assert
         expect(answer).must_equal 3
     end