; updated for Clojure SVN 1309

(defn parse-grid [s]
  (vec (map (fn [line] (vec (map #(Integer. %) (.split line ","))))
            (.split s "\\s+"))))

(defn main [gridstr]
  (let [costs (parse-grid gridstr)
        size (count costs)]
    (loop [min-sums (vec (replicate size (vec (replicate size nil))))
           work-queue (conj clojure.lang.PersistentQueue/EMPTY [0 0])]
      (if (seq work-queue)
        (let [yx (peek work-queue)
              nbs (filter (fn [nyx] (every? #(< -1 % size) nyx))
                          (map #(map + yx %) [[-1 0] [1 0] [0 -1] [0 1]]))
              nbs-costs (seq (filter identity (map #(get-in min-sums %) nbs)))
              newsum (+ (get-in costs yx)
                        (if nbs-costs (apply min nbs-costs) 0))
              oldsum (get-in min-sums yx)]
          (if (or (nil? oldsum) (< newsum oldsum))
            (recur (assoc-in min-sums yx newsum)
                   (apply conj (pop work-queue) nbs))
            (recur min-sums (pop work-queue))))
        (peek (peek min-sums))))))

(def testgrid "131,673,234,103,18
201,96,342,965,150
630,803,746,422,111
537,699,497,121,956
805,732,524,37,331
")

;(prn (time (main testgrid)))
(prn (time (main (slurp "matrix.txt"))))