Add anagram checker challenge

DIRECTORY.md

@@ -8,6 +8,7 @@
 ## Data Structures
   * Arrays
     * [Add Digits](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/add_digits.rb)
+    * [Anagram Checker](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/anagram_checker.rb)
     * [Find All Duplicates In An Array](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/find_all_duplicates_in_an_array.rb)
     * [Find The Highest Altitude](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/find_the_highest_altitude.rb)
     * [Fizz Buzz](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/fizz_buzz.rb)

data_structures/arrays/anagram_checker.rb

@@ -0,0 +1,31 @@
+# Challenge name: Is anagram
+#
+# Given two strings s and t , write a function to determine
+# if t is an anagram of s.
+#
+# Note:
+# You may assume the string contains only lowercase alphabets.
+#
+# Follow up:
+# What if the inputs contain unicode characters?
+# How would you adapt your solution to such case?
+#
+# @param {String} s
+# @param {String} t
+# @return {Boolean}
+
+def is_anagram(s, t)
+end
+
+s = 'anagram'
+t = 'nagaram'
+puts(is_anagram(s, t))
+# => true
+s = 'rat'
+t = 'car'
+puts(is_anagram(s, t))
+# => false
+s = 'a'
+t = 'ab'
+puts(is_anagram(s, t))
+# => false