Interview assignment 10/07/19 (#flatten)

README.md

Interview task made by Stephan Teeuwen

build flatten without using Array#flatten example: [[1,2,[3]],4] to [1,2,3,4]

Testing:

Run following command to test the functioning of the extension method on Array rspec ./flatten_spec.rb --format documentation

Implementation of flatten assignment:

As commented as well in the code, i used the most basic methods i can think of to avoid #each, #flatten and others and make it as plain ruby as possible. Basically what we do is making an recursive loop, to make an infinitly deeply nested array even flattable, it would be the developers responsibility to use this carefully as for sure it's not the optimal way to work with to large array's as this would require memory usage and speed usage testing.

Usage of the new flatten method

We extended the Array class as the method can practically be used on any array and has been tested to work with flat and non flat array's. Besides this there would be a need to require 'array_extensions' if not auto loader is used.

After requiring the right file we can now use the awsome interview_flattener method by calling it on any array we've created. example: [1,2,[3,4]].interview_flattener

array_extensions.rb

# If we build something like a flattener we would build it as an extension of an array, as it would always be used on an array and this way it is a re-usable method. Offcourse depending on the usecase we would need to decide if we make it so dynamic and re-usable.

# By building it this way or in an seperate class we also make it unit-testable
class Array

  # create the extension method
  def interview_flattener    
    # instantiate return value
    retval = []

    # prefferably in such case offcourse we use #flatten or if needed without flatten we loop with #each, but for the sake of the assignment we'll go basic ruby here to avoid build in methods as request, as much as possible 
    for item in self
      
      # Decide if we need to go a level deeper or not.
      if item.kind_of?(Array)
        # Loop trough the deeper array recursively (Note we use += to merge arrays)
        retval += item.interview_flattener()
      else
        # if we get a single value add it straight to the retval variable
        retval << item
      end
    end

    return retval
  end
end

flatten_spec.rb

require 'array_extensions'

describe Array do

  # Basic nested test compared to static result
  it 'it flattens an nested array with Array#interview_flattener' do
    # Make a test array to test this with
    nested_array = [1,[2,3],[4,[5,[6]]],7]
    result = nested_array.interview_flattener()

    expect(result).to eq [1,2,3,4,5,6,7]
  end

  # basic nested test, to compare #flatten output to our method
  it 'it flattens an nested array the same way as Array#flatten with Array#interview_flattener' do
    # Make a test array to test this with
    nested_array = [1,[2,3],[4,[5,[6]]],7]
    result = nested_array.interview_flattener()
    ruby_method_result = nested_array.flatten()

    expect(result).to eq ruby_method_result
  end

  # basic test to test non flatten array's will also output correctly
  it 'it returns an non-nested array with Array#interview_flattener correctly' do
    # Make a test array to test this with
    nested_array = [1,2,3,4,5,6,7]
    result = nested_array.interview_flattener()

    expect(result).to eq nested_array
  end
end