Implementation of a Flatten function in Ruby

flatten.rb

# This gist shows two different implementation of a Flatten function in Ruby.
# The workaround is to do something like the Deep-First Search algorithm to 'visit' all items contained in recursive arrays.
# These items are being added to the returning array after visited.

# First implementation: Recursive.
# The function tests if the object passed as argument is an array.
# If it does, it iterates it recursively, otherwise it adds the element to the visited elements array (acc).
def recursive_flatten(obj, acc = [])
  obj.is_a?(Array) ? obj.each { |i| recursive_flatten(i, acc) } : acc << obj
  acc
end

# Second implementation: Non-recursive.
# Original array is iterated as a stack.
# If an array is found during the iteration, is placed at the front of the stack.
# Iteration ends when stack is empty.
def non_recursive_flatten(array)
  flat = []
  stack = array.map(&:itself)
  until stack.empty?
    item = stack.shift
    item.is_a?(Array) ? item.reverse_each { |i| stack.unshift(i) } : flat << item
  end
  flat
end

# Test method.
if $PROGRAM_NAME == __FILE__
  samples = [
    [1,2,3],
    [1,[2,3],4,5,[6,[7,8],9,[10],[11,[12]],13],14],
    [[1,2],[3,4,5],[],[6,7]],
  ]
  p samples.map(&method(:recursive_flatten))
  p samples.map(&method(:non_recursive_flatten))
end