Implements a method that flattens a nested array, based on recursion.

README.md

my_flatten

Implements a method that flattens a nested array, based on recursion.
Includes several tests that check the method behavior with different arrays.

my_flatten.rb

# Flattens an array of arbitrarily nested arrays of integers into a flat array of integers. 
# e.g. [[1,2,[3]],4] -> [1,2,3,4]. 

def my_flatten(ary, flattened_array=[])
  return flattened_array if ary.empty?

  case ary[0]
  when Fixnum, Integer
    flattened_array.push(ary[0])
  when Array
    flattened_array = my_flatten(ary[0], flattened_array)
  end
  
  return my_flatten(ary[1..-1], flattened_array)
end

my_flatten([1,2,3,[4,5]])

my_flatten_spec.rb

require File.expand_path('../../lib/my_flatten.rb', __FILE__)

describe "my_flatten" do
  it 'should return an array' do
    expect(my_flatten([1])).to be_an Array
  end

  describe 'should return an flattened array' do
    it 'when passing a nested array' do
      expect(my_flatten([1, [2, 3]])).to eq [1, 2, 3]
    end

    it 'when passing a more complex array' do
      expect(my_flatten([1, [2, 3], [4, 5]])).to eq [1, 2, 3, 4, 5]
    end

    it 'when passing other complex nested arrays' do
      expect(my_flatten([1, [2, 3, [4, 5], 6, 7]])).to eq [1, 2, 3, 4, 5, 6, 7]
    end
  end
end