Merge pull request #135 from msaf9/master

PR for Factorial Non-recursive and Non-iterative feature

DIRECTORY.md

@@ -79,6 +79,7 @@
   * [Ceil Test](https://github.com/TheAlgorithms/Ruby/blob/master/maths/ceil_test.rb)
   * [Decimal To Binary](https://github.com/TheAlgorithms/Ruby/blob/master/maths/decimal_to_binary.rb)
   * [Factorial](https://github.com/TheAlgorithms/Ruby/blob/master/maths/factorial.rb)
+  * [Factorial Non-recursive and Non-iterative](https://github.com/TheAlgorithms/Ruby/blob/master/maths/factorial_non_recursive_non_iterative.rb)
   * [Fibonacci](https://github.com/TheAlgorithms/Ruby/blob/master/maths/fibonacci.rb)
   * [Find Max](https://github.com/TheAlgorithms/Ruby/blob/master/maths/find_max.rb)
   * [Find Min](https://github.com/TheAlgorithms/Ruby/blob/master/maths/find_min.rb)

maths/factorial_non_recursive_non_iterative.rb

@@ -0,0 +1,43 @@
+# A ruby program to find factorial of a given integer
+# Factorial of a given integer is defined as the product of all the positive integers less than or equal to the given integer
+# Mathematical representation: n! = n * (n - 1) * (n - 2) * ... * 1
+
+#
+# Non-recursive and non-iterative approach
+#
+
+def factorial(number)
+  if number < 0
+    "Please check your input number! The given number is a negative number."
+  elsif number == 0
+    "The factorial of #{number} is 1."
+  else
+    result = (1..number).inject(:*)
+    "The factorial of #{number} is #{result}."
+  end
+  rescue
+    "Error: Please provide integer only!"
+end
+
+# Valid inputs
+puts factorial(0)
+# The factorial of 0 is 1.
+
+puts factorial(4)
+# The factorial of 4 is 24.
+
+puts factorial(10)
+# The factorial of 10 is 3628800.
+
+puts factorial(1)
+# The factorial of 1 is 1.
+
+puts factorial(-5)
+# Please check your input number! The given number is a negative number.
+
+# Invalid inputs
+puts factorial("a")
+# Error: Please provide integer only!
+
+puts factorial("2")
+# Error: Please provide integer only!