group combinations

gcombo.rb

# solution for problem 1.27 from https://sites.google.com/site/prologsite/prolog-problems/1
def gcombo(list, ns, acc, q = [], rest = list, qg = [])
  if ns.sum != list.size && acc.empty?
    raise ArgumentError, "Impossible to group #{list} into groups of #{ns} elements"
  end

  if ns.empty?
    acc << qg
    return
  end

  return if list.empty?

  n,*nt = ns
  h,*t = list

  return if n == 0 || n > list.size

  s = q + [h]

  1 == n &&
    gcombo(rest - s, nt, acc, [], rest - s, qg + [ s ])

  gcombo(t, [n - 1] + nt, acc, s, rest, qg)
  gcombo(t,           ns, acc,        q, rest, qg)
end

gcombo((1..5).to_a, [2,2,1], acc = [])

pp acc; ''
# => 
# [[[1, 2], [3, 4], [5]],
#  [[1, 2], [3, 5], [4]],
#  [[1, 2], [4, 5], [3]],
#  [[1, 3], [2, 4], [5]],
#  [[1, 3], [2, 5], [4]],
#  [[1, 3], [4, 5], [2]],
#  [[1, 4], [2, 3], [5]],
#  [[1, 4], [2, 5], [3]],
#  [[1, 4], [3, 5], [2]],
#  [[1, 5], [2, 3], [4]],
#  [[1, 5], [2, 4], [3]],
#  [[1, 5], [3, 4], [2]],
#  [[2, 3], [1, 4], [5]],
#  [[2, 3], [1, 5], [4]],
#  [[2, 3], [4, 5], [1]],
#  [[2, 4], [1, 3], [5]],
#  [[2, 4], [1, 5], [3]],
#  [[2, 4], [3, 5], [1]],
#  [[2, 5], [1, 3], [4]],
#  [[2, 5], [1, 4], [3]],
#  [[2, 5], [3, 4], [1]],
#  [[3, 4], [1, 2], [5]],
#  [[3, 4], [1, 5], [2]],
#  [[3, 4], [2, 5], [1]],
#  [[3, 5], [1, 2], [4]],
#  [[3, 5], [1, 4], [2]],
#  [[3, 5], [2, 4], [1]],
#  [[4, 5], [1, 2], [3]],
#  [[4, 5], [1, 3], [2]],
#  [[4, 5], [2, 3], [1]]]