custom_flatten.rb

# Flattens an array of arbitrarily nested arrays into a flat array
def flatten(ar)
	flat_ar = []
	ar.each do |elem|
		if elem.class == Array
		   flat_ar.concat flatten(elem)
		else
			flat_ar << elem
		end
	end
	return flat_ar
end

# simple 'test cases'
p [] == flatten([])
p [1] == flatten([1])
p [1] == flatten([[[1]]])
p [1,2] == flatten([[1],[2]])
p [1,2,3,4] == flatten([1,[2],[3,[4]]])
p [1,2,3,4] == flatten([[[1],2],3,4])
p [1,2,3,4,5,6,7,8,9,10] == flatten([1,2,[3,4],5,[6,[7,8,[9,10]]]])