too clever for me, pure math

2023/src/day18.clj

@@ -0,0 +1,33 @@
+(ns day18 (:require [core :refer [get-puzzle-input]]
+                    [clojure.string :as str]))
+
+(def dir-map {\U [0 -1] \L [-1 0] \R [1 0] \D [0 1]
+              \3 [0 -1] \2 [-1 0] \0 [1 0] \1 [0 1]})
+
+(def input
+  (->> (get-puzzle-input 18)
+       (map #(let [[dir n hex-str] (str/split % #" ")]
+               [(dir-map (last dir))
+                (parse-long n)
+                [(dir-map (last (drop-last hex-str)))
+                 (Long/parseLong (subs hex-str 2 (- (count hex-str) 2))
+                                 16)]]))))
+
+;; Shoelace / Pick's Algorithm, wtf?!
+(defn area [vs]
+  (reduce (fn [[pos ans]
+               [[x y] n]]
+            (let [pos' (+ pos
+                          (* x n))
+                  ans' (+ ans
+                          (* y n pos')
+                          (/ n 2))]
+              [pos' ans']))
+          [0 1]
+          vs))
+
+;; part 1
+(area (map drop-last input))
+
+;; part 2
+(area (map #(% 2) input))