Flatten Array

flatten.rb

def flatten_array(array)
  ans = []
  array&.each do |element|
    if element.is_a? Array
      ans += flatten_array(element)
    else
      ans << element
    end
  end
  ans
end

flatten_spec.rb

#
# run tests using `rspec flatten_spec.rb`

require './flatten'

RSpec.describe "flatten" do
  it do
    input = [[1,2,[3]],4]
    output = [1,2,3,4]
    expect(flatten_array(input)).to eq(output)
  end
  it do
    input = [[1,2,[]],4]
    output = [1,2,4]
    expect(flatten_array(input)).to eq(output)
  end
  it do
    input = [[1,[[],[],[],[]],2,4]]
    output = [1,2,4]
    expect(flatten_array(input)).to eq(output)
  end
  it do
    input = []
    output = []
    expect(flatten_array(input)).to eq(output)
  end
  it do
    input = nil
    output = []
    expect(flatten_array(input)).to eq(output)
  end
end