Adding "Following Integer" solution

open_challenges/hard/following_integer.rb

@@ -0,0 +1,28 @@
+#! /usr/bin/env ruby
+# CodeEval - Hard) Following Integer
+# http://www.codeeval.com/open_challenges/44/
+# author: Rafael Xavier <rxaviers at gmail.com>
+
+class Test
+    def initialize(line)
+        @n = line.strip.to_i
+    end
+
+    def run
+        puts @n.following_integer
+    end
+end
+
+class Integer
+    def following_integer
+        seq = (to_s.chars.to_a + ["0"]).permutation.to_a.sort.uniq.map{|i|
+            i.join('').to_i
+        }
+        seq[ seq.index(self)+1 ]
+    end
+end
+
+File.open(ARGV[0]).each_line do |line|
+    t = Test.new(line)
+    t.run
+end

open_challenges/hard/following_integer.testcases

@@ -0,0 +1,34 @@
+115
+8000
+177115
+206155
+717272
+314920
+812939
+6233
+604888
+2020
+594909
+447631
+80
+374525
+883189
+7007
+68
+88
+202
+2
+301
+41
+103044
+405946
+785741
+440
+656394
+643338
+638561
+495048
+759621
+786884
+208
+689266