flatten an Array

flatten.rb

require 'minitest/autorun'

##
# Implement flatten
#
# ruby -Ilib:test flatten.rb

def flatten(accumulator, element)
  if element.is_a? Array
    element.each {|e| flatten(accumulator, e)}
  else
    accumulator << element
  end
end

class TestFlatten < Minitest::Test
  def test_handles_nested_array
    input = [[1,2,[3]],4]
    result = []
    expected = [1,2,3,4]
    flatten(result, input)
    assert_equal(result, expected)
  end

  def test_handles_flat_array
    input = [1,2,3,4]
    result = []
    expected = [1,2,3,4]
    flatten(result, input)
    assert_equal(result, expected)
  end
end