(with-test
  (defn maximal-path [tree-file]
    (with-open [rdr (BufferedReader. (FileReader. tree-file))]
      (let [lines (reverse
		   (map
		    (fn [x]
		      (map #(Integer. %) (re-seq #"\d+" x)))
		    (line-seq rdr)))]
	(first
	 (reduce
	  (fn [a b]
	    (map max (map + b a) (map + b (rest a))))
	  lines)))))

  (is (= (maximal-path "prob_18.txt") 1074))
  (is (= (maximal-path "prob_67.txt") 7273)))