diff --git a/hamming.rb b/hamming.rb
new file mode 100644
index 0000000..9e33ced
--- /dev/null
+++ b/hamming.rb
@@ -0,0 +1,14 @@
+class Hamming
+
+  def self.compute(a,b)
+    raise ArgumentError unless a.length == b.length
+    self.compute_helper(a,b)
+  end
+
+  def self.compute_helper(a,b)
+    return 0 if a == nil
+    a[0] == b[0] ? value = 0 : value = 1
+    value + self.compute_helper(a[1..-1], b[1..-1])
+  end
+
+end
diff --git a/hamming_test.rb b/hamming_test.rb
index 2d1f9d7..e97bff1 100644
--- a/hamming_test.rb
+++ b/hamming_test.rb
@@ -4,72 +4,67 @@
 
 class HammingTest < Minitest::Test
   def test_identical_strands
-    skip
     assert_equal 0, Hamming.compute('A', 'A')
   end
 
   def test_long_identical_strands
-    skip
     assert_equal 0, Hamming.compute('GGACTGA', 'GGACTGA')
   end
 
   def test_complete_distance_in_single_nucleotide_strands
-    skip
     assert_equal 1, Hamming.compute('A', 'G')
   end
 
   def test_complete_distance_in_small_strands
-    skip
     assert_equal 2, Hamming.compute('AG', 'CT')
   end
 
   def test_small_distance_in_small_strands
-    skip
+
     assert_equal 1, Hamming.compute('AT', 'CT')
   end
 
   def test_small_distance
-    skip
+
     assert_equal 1, Hamming.compute('GGACG', 'GGTCG')
   end
 
   def test_small_distance_in_long_strands
-    skip
+
     assert_equal 2, Hamming.compute('ACCAGGG', 'ACTATGG')
   end
 
   def test_non_unique_character_in_first_strand
-    skip
+
     assert_equal 1, Hamming.compute('AGA', 'AGG')
   end
 
   def test_non_unique_character_in_second_strand
-    skip
+
     assert_equal 1, Hamming.compute('AGG', 'AGA')
   end
 
   def test_large_distance
-    skip
+
     assert_equal 4, Hamming.compute('GATACA', 'GCATAA')
   end
 
   def test_large_distance_in_off_by_one_strand
-    skip
+
     assert_equal 9, Hamming.compute('GGACGGATTCTG', 'AGGACGGATTCT')
   end
 
   def test_empty_strands
-    skip
+
     assert_equal 0, Hamming.compute('', '')
   end
 
   def test_disallow_first_strand_longer
-    skip
     assert_raises(ArgumentError) { Hamming.compute('AATG', 'AAA') }
   end
 
   def test_disallow_second_strand_longer
-    skip
+    
     assert_raises(ArgumentError) { Hamming.compute('ATA', 'AGTG') }
   end
 end