combinations.rb

# get all combinations http://en.wikipedia.org/wiki/Combination
 
n = (ARGV[0] || 5).to_i
m = (ARGV[1] || 3).to_i

puts "#{n}/#{m}"

def comb(list, m, q, acc)
  return if list.empty?

  a, b = list[0,1], list[1..-1]

  acc << (q + a) if m == 1

  comb(b, m - 1, q + a, acc)

  comb(b, m, q, acc)
end

comb((1..n).to_a, m, [], acc = [])

p acc
# Example
# > ruby comb.rb 5 3
# 5/3
# [[1, 2, 3], [1, 2, 4], [1, 2, 5], [1, 3, 4], [1, 3, 5], [1, 4, 5], [2, 3, 4], [2, 3, 5], [2, 4, 5], [3, 4, 5]]