main.rb

steps = 5

(1..steps)
  .map { |x| (1..steps-1).map { |y| [x, y] } }
  .flatten(1)
  .select { |x, y| steps - x - y > 0 }
  .group_by { |x, y| x }
  .each do |x, sets|
    sets.each do |x, y|
      puts [x, y].inspect
    end
    puts
  end