A coding demo for a job application at Theorem, LLC. "Write some code, that will flatten an array of arbitrarily nested arrays of integers into a flat array of integers."

demo.rb

# Here's a function to 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].
#
# This was written for Ruby 2
#
# Invoke this function by passing it the array to be flattened in the
# "input" argument and leaving the "output" argument nil.
# 
# E.g.
# >> recursive_flatten([[1,2,[3]],4])
def recursive_flatten(input, output=nil)
    output ||= []
    for value in input
        if value.is_a? Integer
            output << value
        elsif value.is_a? Array
            recursive_flatten(value, output)
        else
            raise 'Error. All array items must be Integers or Arrays. Got %s' % value.class.name
        end
    end
    output
end