flatten_array.rb

# Write some code, that will flatten an array of arbitrarily nested arrays of integers into a flat array of integers. 
# e.g. [[1,2,[3]],4] -> [1,2,3,4].


# SOLUTION
class Array
  def flatten_array(number = nil)
    number ? multiple_flatten(self, number) : recursive_flatten(self)
  end

  private

  def recursive_flatten(array, results = [])
    array.each do |element|
      if element.class == Array
        recursive_flatten(element, results)
      else
        next unless element.is_a? Integer
        results << element
      end
    end
    results
  end

  def multiple_flatten(array, number)
    count = 0
    arr = array
    until count >= number
      arr = single_flatten(arr)
      count += 1
    end
    arr
  end

  def single_flatten(array)
    results = []
    array.each do |element|
      if element.class == Array
        element.each { |value| results << value }
      else
        next unless element.is_a? Integer
        results << element
      end
    end
    results
  end
end

# p [1, 2, [3, [4, 5]], 6, [7, 8], 9].flatten_array #=> [1, 2, 3, 4, 5, 6, 7, 8, 9]
# p [1, 2, [3, [4, 5]], 6, [7, 8], 9].flatten_array(1) #=> [1, 2, 3, [4, 5], 6, 7, 8, 9]
# p [].flatten_array #=> []
# p [1, 2, 3, 4].flatten_array #=> [1, 2, 3, 4]
# p [1, 2, [3, [4, 5, [6, 7]]], 8, [9, 10], 11].flatten_array(2) #=> [1, 2, 3, 4, 5, [6, 7], 8, 9, 10, 11]
# p [1, 2, [3, [4, 5, [6, 7]]], 8, [9, 10], 11].flatten_array(3) #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
# p [1, 2, 3, 4, 'one', :sss].flatten_array(3) #=> [1, 2, 3, 4]

# RSpec Exception Test
RSpec. describe Array do
  it 'flattens array' do
    array = [1, 2, [3, [4, 5]], 6, [7, 8], 9]
    array = array.flatten_array
    expect(array).to eq([1, 2, 3, 4, 5, 6, 7, 8, 9])
  end

  it 'flattens array at a given nesting level as an argument' do
    array = [1, 2, [3, [4, 5]], 6, [7, 8], 9]
    array = array.flatten_array(1)
    expect(array).to eq([1, 2, 3, [4, 5], 6, 7, 8, 9])
  end

  it 'does not leave out any given nest level un-flattened' do
    array = [1, 2, [3, [4, 5]], 6, [7, 8], 9]
    array = array.flatten_array
    expect(array).not_to eq([1, 2, 3, [4, 5], 6, 7, 8, 9])
  end

  it 'returns empty Array' do
    array = []
    array = array.flatten_array
    expect(array).to be_empty
  end

  it 'must be an instance of Array' do
    array = [1, 2, 3, 4]
    array = array.flatten_array
    expect(array).to be_an_instance_of(Array)
  end
  
  it 'removes string and symbols from the array and flattens the array' do
    array = [1, 2, 3, 4, 'one', :sss]
    array = array.flatten_array
    expect(array).to eq([1, 2, 3, 4])
  end
end