Exercism-74 Atbash Cipher

Author: kumar91gopi

README.md

@@ -295,6 +295,8 @@ solution of many challenges of [Leetcode](https://leetcode.com/), [Exercism](htt
 71. [Protein Translation](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/protein_translation.rb)
 72. [Wordy](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/wordy.rb)
 73. [Secret Handshake](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/secret_handshake.rb)
+74. [Atbash Cipher](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/atbash_cipher.rb)
+
 
 <a name="leetcode"/>
 

exercism/atbash_cipher.rb

@@ -0,0 +1,58 @@
+# Problem: https://exercism.org/tracks/ruby/exercises/atbash-cipher
+
+# Solution
+class Atbash
+    LETTERS = ("a".."z").to_a
+
+    def self.encode(plaintext)
+      return "" if plaintext == ""
+      ciphertext = ""
+      plaintext = plaintext.downcase
+      curr_cipher_len = 0
+      for i in 0...(plaintext.length)
+        if curr_cipher_len==5
+          ciphertext+=" "
+          curr_cipher_len = 0
+        end 
+        
+        if plaintext[i].match(/\d+/)
+          ciphertext+=plaintext[i]
+          curr_cipher_len+=1
+          next
+        end
+        
+        unless LETTERS.index(plaintext[i]).nil?
+          ciphertext+= LETTERS[25-LETTERS.index(plaintext[i])]
+          curr_cipher_len+=1
+        end
+      end
+      ciphertext.strip
+    end
+
+    def self.decode(ciphertext)
+      return "" if ciphertext == ""
+      plaintext = ""
+      ciphertext = ciphertext.gsub(" ","")
+      ciphertext.chars.each do |char|
+        if LETTERS.index(char).nil?
+          plaintext+=char
+        else
+          plaintext+= LETTERS[25-LETTERS.index(char)]
+        end
+      end
+      plaintext
+    end
+end
+  
+# Solution(idiomatic ruby)
+lass Atbash
+  ALPHA = ('a'..'z').to_a.join
+  
+  def self.encode(text)
+    decode(text).chars.each_slice(5).map(&:join).join(' ')
+  end
+
+  def self.decode(text)
+    text.downcase.gsub(/\W/, '').tr(ALPHA, ALPHA.reverse)
+  end
+end