flatten.rb

def flatten(input)
  result = Array.new
  input.each do |element|
    if element && element.instance_of?(Array)
      # if the current element is an array then recursively flatten that
      # array and add that array to the result
      result = result+flatten(element)
    else
      # else this is just a regular element and add the element to result
      result << element
    end
  end
  return result
end

input = [[1,2,[3]],4]
print flatten(input)