day 17 start

1 files changed, 51 insertions, 0 deletions

diff --git a/aoc2023-other/day-17/day-17.rkt b/aoc2023-other/day-17/day-17.rkt
new file mode 100644
index 0000000..8a1fc02
--- /dev/null
+++ b/aoc2023-other/day-17/day-17.rkt
@@ -0,0 +1,51 @@
+#lang racket
+
+(require advent-of-code
+         threading)
+
+(struct posn (r c) #:transparent)
+(struct to (posn dir) #:transparent)
+(struct edge (from to dir) #:transparent)
+
+(define input
+  "2413432311323
+3215453535623
+3255245654254
+3446585845452
+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533")
+
+(define grid
+  (for*/hash ([(row r) (in-indexed (in-list (string-split input "\n")))]
+              [(col c) (in-indexed (in-string row))])
+    (values (posn r c) (~> col string string->number))))
+
+(define grid-nodes (hash-keys grid))
+(match-define (posn rmax cmax) (argmax (λ (p) (+ (posn-r p) (posn-c p))) grid-nodes))
+
+(define/match (find-edge-cost e prev-two)
+  [((edge _ _ d) (list d d)) 1e10]
+  [(_ _) (hash-ref edges e)])
+
+(define (find-node-cost p)
+  (match-define (posn r c) p)
+  (+ (- rmax r) (- cmax c)))
+
+(define (neighbors p)
+  (match-define (posn r c) p)
+  (~>> (list (to (posn (sub1 r) c) 'north)
+             (to (posn (add1 r) c) 'south)
+             (to (posn r (add1 c)) 'east)
+             (to (posn r (sub1 c)) 'west))
+       (filter (λ (p) (hash-has-key? grid (to-posn p))))))
+
+(define edges
+  (for*/hash ([(k v) (in-hash grid)] [neighbor (in-list (neighbors k))])
+    (values (edge k (to-posn neighbor) (to-dir neighbor)) v)))