EuclideanRhythm.rb

# @author https://github.com/kn1kn1/EuclideanRhythm
# @see http://cgm.cs.mcgill.ca/~godfried/publications/banff.pdf
module EuclideanRhythm
  extend self

  def euclidean_rhythm(pulses, steps)
    steps  = steps.to_i
    pulses = pulses.to_i

    return [true] * steps if pulses >= steps

    if steps - pulses == 1
      # WORKAROUND for the following cases
      #  E(2,3)=[x . x]
      #  E(3,4)=[x . x x]
      #  E(5,6)=[x . x x x x]
      pat    = [true] * steps
      pat[1] = false
      return pat
    end

    groups = []
    for i in 0...steps
      val = i < pulses ? true : false
      groups.push([val])
    end

    while (l = groups.count - 1) != 0
      ub    = 0
      first = groups[0]
      ub    += 1 while first == groups[ub]
      break if ub >= l

      lb   = l
      last = groups[l]
      lb   -= 1 while last == groups[lb]
      break if lb <= 0

      count  = [ub, l - lb].min
      groups = groups[0..(count - 1)]
                 .each_with_index.map { |e, i| e.concat(groups[l - i]) }
                 .concat(groups[count..(-count - 1)])
    end
    groups.flatten
  end
end