diff --git a/hamming.rb b/hamming.rb
new file mode 100644
index 0000000..58ed912
--- /dev/null
+++ b/hamming.rb
@@ -0,0 +1,34 @@
+class Hamming
+  def self.compute(first_strand, second_strand)
+
+    first_strand = first_strand.chars
+    second_strand = second_strand.chars
+    
+    # error handling 
+    if first_strand.length != second_strand.length
+      raise ArgumentError, "Strands must be the same length."
+    end
+
+    difference = 0 
+    recursion(first_strand,second_strand, difference)
+  end
+
+  def self.recursion(first_strand, second_strand, difference)
+    # base case
+    if first_strand.empty? || second_strand.empty? 
+      return difference
+    end 
+    
+    if first_strand[0] == second_strand[0]
+      difference += 0
+      first_strand.shift
+      second_strand.shift
+      recursion(first_strand, second_strand, difference)
+    else first_strand[0] != second_strand[0]
+      difference += 1 
+      first_strand.shift
+      second_strand.shift
+      recursion(first_strand, second_strand, difference)
+    end 
+  end 
+end
diff --git a/hamming_test.rb b/hamming_test.rb
index 2d1f9d7..0ddf0a1 100644
--- a/hamming_test.rb
+++ b/hamming_test.rb
@@ -4,72 +4,58 @@
 
 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