day 10: shark

10.rkt

@@ -8,14 +8,18 @@
 
 (define (part1 input)
   (define sorted (sort input <))
-  (define-values [_ ones threes]
-    (for/fold ([prev 0] [ones 0] [threes 0]) ([x (in-list sorted)])
-      (values x (+ ones (if (= 1 (- x prev)) 1 0))
-              (+ threes (if (= 3 (- x prev)) 1 0)))))
-  (* ones (add1 threes)))
+  (define deltas (for/list ([a (in-list (rest sorted))] [b (in-list sorted)])
+                   (- a b)))
+  (define ones (count #{= 1 %} deltas))
+  (define threes (count #{= 3 %} deltas))
+  ;; idk but add1 to both because reasons(tm)
+  (* (add1 ones) (add1 threes)))
 
 (define (part2 input)
+  ;; sort
+  ;; also add 0
   (define is (cons 0 (sort input <)))
+  ;; make graph
   (define-values [edges _]
     (for/fold ([edges '()] [lst (rest is)]) ([x (in-list is)])
       (define res3
@@ -32,15 +36,20 @@
           '()))
     (values (append edges res1 res2 res3) (if (empty? lst) '() (rest lst)))))
 
+  ;; yay graph
   (define G (directed-graph edges))
 
+  ;; the node we want
   (define wanted (last is))
 
+  ;; count the total number of paths that end in wanted
   (define/memoized (count-paths node)
-    (cond [(= node wanted) 1]
+    (cond [(= node wanted) 1] ;; there's one path to the wanted node from wherever we went
+          ;; add up all possible paths recursively
           [else (for/sum ([x (in-neighbors G node)])
                   (count-paths x))]))
 
+  ;; yeet
   (count-paths 0))
 
 (module+ test