prep for 2023, renaming for consistency

1 files changed, 56 insertions, 0 deletions

diff --git a/aoc2020/day-12/day-12.rkt b/aoc2020/day-12/day-12.rkt
new file mode 100644
index 0000000..e4bbd32
--- /dev/null
+++ b/aoc2020/day-12/day-12.rkt
@@ -0,0 +1,56 @@
+#lang rackjure
+
+(require advent-of-code
+         threading
+         (only-in relation ->symbol ->number))
+
+(struct instruction (direction distance) #:transparent)
+
+(define (parse-instruction str)
+  (match str
+    [(regexp #px"(\\w)(\\d+)" (list _ dir dist)) (instruction (->symbol dir) (->number dist))]))
+
+(define instructions
+  (~>> (fetch-aoc-input (find-session) 2020 12) string-split (map parse-instruction)))
+
+;; part 1
+(struct boat (x y nav) #:transparent)
+
+(define (angle->direction n)
+  (case n
+    [(0) 'E]
+    [(90) 'N]
+    [(180) 'W]
+    [(270) 'S]))
+
+(define (move-via-direct-command inst b)
+  (match-define (boat x y facing) b)
+  (match inst
+    [(instruction 'N n) (boat x (+ y n) facing)]
+    [(instruction 'S n) (boat x (- y n) facing)]
+    [(instruction 'E n) (boat (+ x n) y facing)]
+    [(instruction 'W n) (boat (- x n) y facing)]
+    [(instruction 'L n) (boat x y (modulo (+ facing n) 360))]
+    [(instruction 'R n) (boat x y (modulo (- facing n) 360))]
+    [(instruction 'F n) (move-via-direct-command (instruction (angle->direction facing) n) b)]))
+
+(define (find-boat-destination using start instructions)
+  (match-define (boat x y _) (foldl using start instructions))
+  (+ (abs x) (abs y)))
+
+(find-boat-destination move-via-direct-command (boat 0 0 0) instructions)
+
+;; part 2
+(define (move-via-waypoint inst b)
+  (match-define (boat x y (cons wp-x wp-y)) b)
+  (match inst
+    [(instruction 'N n) (boat x y (cons wp-x (+ wp-y n)))]
+    [(instruction 'S n) (boat x y (cons wp-x (- wp-y n)))]
+    [(instruction 'E n) (boat x y (cons (+ wp-x n) wp-y))]
+    [(instruction 'W n) (boat x y (cons (- wp-x n) wp-y))]
+    [(instruction _ 180) (boat x y (cons (- wp-x) (- wp-y)))]
+    [(or (instruction 'L 90) (instruction 'R 270)) (boat x y (cons (- wp-y) wp-x))]
+    [(or (instruction 'R 90) (instruction 'L 270)) (boat x y (cons wp-y (- wp-x)))]
+    [(instruction 'F n) (boat (+ x (* n wp-x)) (+ y (* n wp-y)) (cons wp-x wp-y))]))
+
+(find-boat-destination move-via-waypoint (boat 0 0 '(10 . 1)) instructions)