dogenpunk · December 14, 2016 03:11 · Dec 14, 2016
diff --git a/flatten.rb b/flatten.rb
@@ -0,0 +1,54 @@
+=begin rdoc
+Takes any nested combination of Arrays and returns their contents as a
+single Array. my_flatten(nil) returns an empty Array.
+=end
+
+def my_flatten values=[]
+  raise "`my_flatten' requires an Array argument." unless values.is_a?(Array)
+
+  result = []
+  values.each do |v|
+    if v.is_a?(Array)
+      result.concat my_flatten(v)
+    else
+      result << v unless v.nil?
+    end
+  end
+
+  result
+end
+
+if __FILE__ == $0
+  require 'minitest/autorun'
+  require 'minitest/pride'
+
+  class MyFlattenTest < MiniTest::Unit::TestCase
+    def test_flattens_to_arbitrary_depth
+      result = my_flatten([1, [2, 3], 4, [[5, 6, [7], 8], 9, 10], 11])
+
+      assert_equal [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], result
+    end
+
+    def test_raises_exception_when_passed_non_array
+      assert_raises RuntimeError do
+        my_flatten(a: 1, b: [2])
+      end
+    end
+
+    def test_eliminates_empty_arrays
+      result = my_flatten([1, [], 2, [3]])
+
+      assert_equal [1, 2, 3], result
+    end
+
+    def test_eliminates_nils
+      result = my_flatten([1, nil, 3])
+
+      assert_equal [1, 3], result
+    end
+
+    def returns_an_empty_array_when_called_with_no_argument
+      assert_equal [], my_flatten
+    end
+  end
+end
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