1 files changed, 48 insertions, 0 deletions
diff --git a/racket/aoc2023/day-18/day-18.rkt b/racket/aoc2023/day-18/day-18.rkt
new file mode 100644
index 0000000..b589e41
--- /dev/null
+++ b/racket/aoc2023/day-18/day-18.rkt
@@ -0,0 +1,48 @@
+#lang racket
+(require advent-of-code
+         threading)
+
+(struct coord (x y))
+
+(define input (~> (fetch-aoc-input (find-session) 2023 18 #:cache #true)))
+
+(define (go-to-next-coord c dir dist)
+  (match-define (coord x y) c)
+  (match dir
+    [(or "R" "0") (coord (+ x dist) y)]
+    [(or "D" "1") (coord x (- y dist))]
+    [(or "L" "2") (coord (- x dist) y)]
+    [(or "U" "3") (coord x (+ y dist))]))
+
+(define/match (triangle-area _coord1 _coord2)
+  [((coord x1 y1) (coord x2 y2)) (/ (- (* x1 y2) (* x2 y1)) 2)])
+
+(define (find-area-using parser)
+  (for/fold ([area 0]
+             [perimeter 0]
+             [current-coord (coord 0 0)]
+             #:result (+ 1 (abs area) (/ perimeter 2)))
+            ([dig (in-list (string-split input "\n"))])
+    (define-values (dir dist) (parser dig))
+    (define next-coord (go-to-next-coord current-coord dir dist))
+    (values (+ area (triangle-area current-coord next-coord)) 
+            (+ perimeter dist) next-coord)))
+
+;; part 1
+(define (parse-front dig)
+  (match-define (regexp #rx"(.) (.*) \\((.*)\\)" 
+                        (list _ dir (app string->number dist) _hex)) 
+    dig)
+  (values dir dist))
+
+(find-area-using parse-front)
+
+;; part 2
+
+(define (parse-hex dig)
+  (match-define (regexp #rx".*\\(#(.....)(.)\\)" 
+                        (list _ (app (curryr string->number 16) dist) dir))
+    dig)
+  (values dir dist))
+
+(find-area-using parse-hex)