Flatten array ruby solution.

solutions/ruby/flatten_array.rb

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+# Note that there is already an implementation in the core ruby library
+# http://ruby-doc.org/core-2.2.0/Array.html#method-i-flatten
+
+def flatten_array(arr = [])
+  return arr unless arr.is_a? Array
+
+  result = []
+  arr.each do |elem|
+    if elem.is_a? Array
+      result += flatten_array(elem)
+    else
+      result << elem
+    end
+  end
+
+  result
+end
+
+flatten_array([]) # => []
+flatten_array([[["a"]]]) # => ["a"]
+flatten_array([0, ["damn"], [[["a", "b"]]], 0]) # => [0, "damn", "a", "b", 0]