euler18and67.rb

require "enumerator"

# tree is represented as: [[a,b,c,d],[e,f,g],[h,i],[j]]
# (bottom up) 
#
def max(tree)
  bottom = tree.shift
  pairs = bottom.enum_for(:each_cons, 2).to_a
  update = pairs.enum_for(:each_with_index).map do |pair,i|
    tree.first[i] + pair.max
  end
  
  tree.first.replace(update)
  tree.length > 1 ? max(tree) : tree.flatten.first 
end