Ports - Steph

lib/fibonacci.rb

@@ -5,8 +5,37 @@
 # ....
 # e.g. 6th fibonacci number is 8
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(1)
+
+# RECURSIVE SOLUTION
 def fibonacci(n)
-  raise NotImplementedError
+  raise ArgumentError if n.nil? || n < 0
+  if n == 0 
+    return 0
+  end
+
+  if n == 1
+    return 1
+  end
+
+  return fibonacci(n-1) + fibonacci(n-2)
 end
+
+
+# ITERATIVE SOLUTION
+
+def fibonacci(num)
+  raise ArgumentError if num.nil? || num < 0
+
+  x = 0
+  y = 1
+
+  num.times do
+    sum = x + y
+    x = y
+    y = sum
+  end
+
+  return x
+end