janet/examples/maxtriangle.dst

# Find the maximum path from the top (root)
# of the triangle to the leaves of the triangle.
  
(defn vmap2 [f m1 m2] 
 (def len (length m1))
 (def arr @[])
 (for [i 0 len] (array-push arr (f (get m1 i) (get m2 i))))
 arr)

(defn reduce [s f c]
 (var res s)
 (for [i 0 (length c)]
  (:= res (f res (get c i))))
 res)

(defn max1 [l r] (if (< l r) r l))
    
(defn myfold [xs ys]
 (def xs1 (tuple-prepend xs 0))
 (def xs2 (tuple-append xs 0))
 (def m1 (vmap2 + xs1 ys))
 (def m2 (vmap2 + xs2 ys))
 (vmap2 max1 m1 m2))

(defn max [a]
 (var m (get a 0))
 (for [i 0 (length a)]
  (if (< m (get a i))
   (:= m (get a i))))
 m)

(defn maxpath [t]
 (max (reduce () myfold t)))

(def triangle @[
 @[3]
 @[7 10]
 @[4 3 7]
 @[8 9 1 3]
])

(print (maxpath triangle))