day 11 racket complete

1 files changed, 36 insertions, 0 deletions

diff --git a/aoc2023-other/day-11/day-11.rkt b/aoc2023-other/day-11/day-11.rkt
new file mode 100644
index 0000000..883ae11
--- /dev/null
+++ b/aoc2023-other/day-11/day-11.rkt
@@ -0,0 +1,36 @@
+#lang racket
+
+(require advent-of-code
+         threading)
+
+(struct posn (x y) #:transparent)
+
+(define input
+  (~> (fetch-aoc-input (find-session) 2023 11 #:cache #true)
+      (string-split "\n")
+      (map string->list _)))
+
+(define (get-empty-ranks grid)
+  (for/list ([(rank n) (in-indexed grid)] #:when (equal? '(#\.) (remove-duplicates rank)))
+    n))
+
+(define (count-prior-empty-ranks rank empty-ranks)
+  (~> empty-ranks (takef (curryr < rank)) length))
+
+(define empty-rows (get-empty-ranks input))
+(define empty-columns (get-empty-ranks (apply map list input))) ;; transpose
+
+(define (sum-of-star-distances in expand-by)
+  (define stars
+    (for*/list ([(row x) (in-indexed in)] [(col y) (in-indexed row)] #:when (equal? col #\#))
+      (posn (+ x (* (sub1 expand-by) (count-prior-empty-ranks x empty-rows)))
+            (+ y (* (sub1 expand-by) (count-prior-empty-ranks y empty-columns))))))
+  (for/sum ([star-pair (in-combinations stars 2)])
+           (match-define (list (posn x1 y1) (posn x2 y2)) star-pair)
+           (+ (abs (- x1 x2)) (abs (- y1 y2)))))
+
+;; part 1
+(sum-of-star-distances input 2)
+
+;; part 2
+(sum-of-star-distances input 1000000)