diff --git a/lib/factorial.rb b/lib/factorial.rb
index 6a4a408..9baf1f8 100644
--- a/lib/factorial.rb
+++ b/lib/factorial.rb
@@ -1,6 +1,54 @@
 # Computes factorial of the input number and returns it
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: Linear or O(n) where n is the number input 
+# Space complexity: Constant or O(1), will have the same  number of variables no matter the size of the input 
+
 def factorial(number)
-  raise NotImplementedError
+return 1 if number == 0 
+if number == nil 
+  raise ArgumentError, "Enter an integer"
+end 
+a = 1
+b = number 
+while a < number
+  b = b * (number - a)
+  a += 1
+end 
+return b 
 end
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+