Array Flattener Implementation

array_flattener.rb

# frozen_string_literal: true
# ArrayFlattener provides a method called `flatten_array` which returns a flat array
# from an array of nested arrays.
class ArrayFlattener
  # The method uses a local variable
  # as a memory object and passes it
  # to the recursive method `recursive_flatten`
  def flatten_array(arr)
    result = []
    recursive_flatten(arr, result)
    result
  end

  private

  # This method loops through the array
  # and adds any element to the memory
  # which isn't of Enumerable type and
  # calls itself on elements which are Enumerable
  def recursive_flatten(arr, memo)
    if arr.is_a? Enumerable
      arr.each do |element|
        recursive_flatten(element, memo)
      end
    else
      memo << arr
    end
  end
end

test_array_flattener.rb

# frozen_string_literal: true
require 'minitest/autorun'

# Defines a test suite and acceptance criteria for the class ArrayFlattener
class TestArrayFlattener < Minitest::Test
  def setup
    @flattener = ArrayFlattener.new
  end

  def test_example_array
    arr = [[1, 2, [3]], 4]
    assert_equal [1, 2, 3, 4], @flattener.flatten_array(arr)
  end

  def test_3_level_deep
    arr = [1, 2, [3, 4, [5], [6, 7]], 8]
    assert_equal [1, 2, 3, 4, 5, 6, 7, 8], @flattener.flatten_array(arr)
  end

  def test_super_deep_array
    arr = [[[[[[[[[[[[1, 2, 3, [4, [5], 6], 7]]]]]]]]]]]]
    assert_equal [1, 2, 3, 4, 5, 6, 7], @flattener.flatten_array(arr)
  end

  def test_empty_array
    arr = []
    assert_equal [], @flattener.flatten_array(arr)
  end

  def test_single_number
    arr = 1
    assert_equal [1], @flattener.flatten_array(arr)
  end
end

test_results.txt

Run options: --seed 53704

# Running:

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Finished in 0.001275s, 3921.9470 runs/s, 3921.9470 assertions/s.
5 runs, 5 assertions, 0 failures, 0 errors, 0 skips