Headers

heads.rb

require 'pp'

h = [1, 2, 3, 1, 2, 3, 2, 1, 3, 2, 1]

opened = []

r = h.inject("") do |a, x|
  # close tags if needed
  while opened.last != nil && opened.last >= x
    a << "</h#{opened.pop}>"
  end
  # open tag
  a << "<h#{x}>"
  # and push to opened stack
  opened << x
  pp opened
  a
end

# close left tags
r << opened.map{|t| "</h#{t}>"}.join

pp r

output.txt

[1]
[1, 2]
[1, 2, 3]
[1]
[1, 2]
[1, 2, 3]
[1, 2]
[1]
[1, 3]
[1, 2]
[1]
"<h1><h2><h3></h3></h2></h1><h1><h2><h3></h3></h2><h2></h2></h1><h1><h3></h3><h2></h2></h1><h1></h1>"