exercism 79 Rotational Cipher

Author: kumar91gopi

README.md

@@ -304,6 +304,7 @@ solution of many challenges of [Leetcode](https://leetcode.com/), [Exercism](htt
 76. [List Ops](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/list_ops.rb)
 77. [Simple Linked List](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/simple_linked_list.rb)
 78. [Binary Search Tree](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/binary_search_tree.rb)
+79. [Rotational Cipher](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/rotational_cipher.rb)
 
 <a name="leetcode"/>
 

exercism/rotational_cipher.rb

@@ -0,0 +1,20 @@
+# Problem: https://exercism.org/tracks/ruby/exercises/rotational-cipher
+
+# Solution
+class RotationalCipher
+    LETTERS = ("a".."z").to_a
+    
+    def self.rotate(input,key)
+      ciphertext=""
+      input.chars.each do |char|
+        if LETTERS.include?(char)
+          ciphertext+=LETTERS[(LETTERS.index(char)+key)%26]
+        elsif LETTERS.include?(char.downcase)
+          ciphertext+=LETTERS[(LETTERS.index(char.downcase)+key)%26].upcase
+        else
+          ciphertext+=char 
+        end
+      end
+        ciphertext
+    end
+end