018.clj

(def triangle [[75]
               [95 64]
               [17 47 82]
               [18 35 87 10]
               [20  4 82 47 65]
               [19  1 23 75  3 34]
               [88  2 77 73  7 63 67]
               [99 65  4 28  6 16 70 92]
               [41 41 26 56 83 40 80 70 33]
               [41 48 72 33 47 32 37 16 94 29]
               [53 71 44 65 25 43 91 52 97 51 14]
               [70 11 33 28 77 73 17 78 39 68 17 57]
               [91 71 52 38 17 14 91 43 58 50 27 29 48]
               [63 66  4 68 89 53 67 30 73 16 69 87 40 31]
               [ 4 62 98 27 23  9 70 98 73 93 38 53 60  4 23]])

;; (partition 2 1 a) splits a into len(a) - 1 two element tuples.
;; take the max of each tuple.
;; b is the next row of the triangle, and len(b) = len(a) - 1
;; merge the (max (partition a) with b, and repeat by partioning etc the result
;; and merging into the next row
(defn merge-rows[a b]
  (map + (map #(apply max %) (partition 2 1 a)) b))

(time (println (reduce merge-rows (reverse triangle))))