>
def comb(n,m)
  stack = Array.new(m)
  count = 0
  (1..n).each do |a|
    (a..n).each do |i|
      stack.clear
      stack.push(a)
      count = 1
      ((i+1)..(n+1)).each do |j|
        if count == m then
          count -= 1
          puts stack.to_s
          stack.pop
        end
          stack.push(j)
          count+=1
      end
    end
  end
end
 
comb(5,3)
</blockcode>

>
 
def comb(n,m)
    result = []
    start = Array.new(m)
    max = Array.new(m)
    0.upto(m-1) do |i| 
        start[i] = i+1
        max[i] = (n-m+i+1)
    end
    result << "["+ start.join(",")+"]"
    while start[0] < max[0]
        last_change = m-1
        start[m-1]+=1
        (m-1).downto(1) do |i|
            if start[i] > max[i] then
                start[i-1]+=1
                last_change = i-1
            else 
                break
            end
        end
        (last_change).upto(m-2) do |i|
            start[i+1] = start[i]+1
        end
        result << "["+ start.join(",")+"]"
    end
"["+result.join(",")+"]"
end
print "Enter n: "
n = gets.to_i
print "Enter m: "
m = gets.to_i
print comb(n,m)+"\n"
</blockcode>

comb xs cnt
   | cnt == 0  = [[]]
   | otherwise = [x:ys | x <- xs, ys <- comb (dropWhile (<= x) xs) (cnt - 1)]

class Integer
  def cartesian(xs)
    xs.map do |n|
      [self, n].flatten
    end
  end
end

irb(main):023:0> 2.cartesian [3,4,5]
[[2, 3], [2, 4], [2, 5]]

def comb(xs,m)
  return xs if m == 1
  xs.inject([]) do |acc, x|
    acc + x.cartesian(comb(xs.select{|n| n > x}, m-1))
  end  
end
 
irb(main):066:0> comb [1,2,3,4,5], 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]]