day 12 complete

1 files changed, 45 insertions, 0 deletions

diff --git a/2022/day-12/day-12.rkt b/2022/day-12/day-12.rkt
new file mode 100644
index 0000000..9120468
--- /dev/null
+++ b/2022/day-12/day-12.rkt
@@ -0,0 +1,45 @@
+#lang racket
+
+(require advent-of-code
+         fancy-app
+         graph)
+
+(define raw-terrain (fetch-aoc-input (find-session) 2022 12 #:cache #true))
+(define special-points (make-hash))
+
+(define terrain-mesh
+  (for*/hash ([(row x) (in-indexed (string-split raw-terrain))] [(col y) (in-indexed row)])
+    (case col
+      [(#\S)
+       (hash-set! special-points 'start (cons x y))
+       (values (cons x y) 0)]
+      [(#\E)
+       (hash-set! special-points 'end (cons x y))
+       (values (cons x y) 25)]
+      [else (values (cons x y) (- (char->integer col) (char->integer #\a)))])))
+
+(define (neighbors p)
+  (match-define (cons x y) p)
+  (for*/list ([dx (in-list '(-1 0 1))]
+              [dy (in-list '(-1 0 1))]
+              #:when (= 1 (abs (+ dx dy)))
+              #:do [(define p (cons (+ x dx) (+ y dy)))]
+              #:when (hash-has-key? terrain-mesh p))
+    p))
+
+(define paths
+  (directed-graph (for*/list ([p (in-list (hash-keys terrain-mesh))]
+                              [neighbor (in-list (neighbors p))]
+                              #:unless (> (sub1 (hash-ref terrain-mesh neighbor))
+                                          (hash-ref terrain-mesh p)))
+                    (list p neighbor))))
+
+;; part 1
+(match-define-values (distances _) (dijkstra paths (hash-ref special-points 'start)))
+(hash-ref distances (hash-ref special-points 'end))
+
+;; part 2
+(for/lists (lengths #:result (apply min lengths))
+           ([start (in-list (hash-keys terrain-mesh))] #:when (= 0 (hash-ref terrain-mesh start)))
+           (match-define-values (distances _) (dijkstra paths start))
+           (hash-ref distances (hash-ref special-points 'end)))