ナムドット問題僕の回答 出力の行数を減らすためにSetを使ってる。

gistfile1.rb

require 'set'
k = [0]*5; m = [0]*5
begin
  puts Set.new([*1..5]).divide{|i| k[i-1]}.map{|i| i.to_a*""}*"."
end while
  (if i = [4,3,2,1].index{|i| k[i] <= m[i-1]}; then i=4-i
  k[i]+=1; m[i] = m[i]>k[i] ? m[i] : k[i]
  ((i+1)..4).each{|j| k[j] = k[0]; m[j] = m[i]; } 
  end)