flatten.rb

require 'rspec'
def flatten(array)
  ret = []
  array.each do |i|
    if i.is_a?(Array)
      ret += flatten(i)
      next
    end
    ret << i
  end
  ret
end

describe '#flatten' do
  it 'should flatten a given array' do
    expect(flatten([[1,2,[3]],4])).to eq([1,2,3,4])
  end

  it 'should flatten the array regardless of the level of nesting' do
    expect(flatten([[1,2,[3,5,[6,7]]],4])).to eq([1,2,3,5,6,7,4])
  end
end