day 18

2024/src/day18.clj

@@ -0,0 +1,59 @@
+(ns day18
+  (:require
+   [clojure.set :refer [union]]
+   [clojure.string :as str]
+   [core :as c]
+   input-manager))
+
+(def N 1024)
+
+(do
+  (def input (->> (input-manager/get-input 2024 18)
+                  (map c/split-on-comma)
+                  (c/n-mapv 2 parse-long)))
+
+  (def walls (->> input
+                  (take N)
+                  (apply hash-set)))
+
+  (def end [(->> input
+                  (take N)
+                 (apply max-key first)
+                 first)
+            (->> input
+                  (take N)
+                 (apply max-key second)
+                 second)]))
+
+(defn in-bounds? [[x y]]
+  (and (>= x 0) (<= x (first end))
+       (>= y 0) (<= y (second end))))
+
+(defn potential-steps [[x y]]
+  [[(inc x) y]
+   [(dec x) y]
+   [x (inc y)]
+   [x (dec y)]])
+
+;; part 1
+(loop [n 0
+       q #{[0 0]}
+       visited #{[0 0]}]
+  (when-not (empty? q)
+    (if (q end)
+      n
+      (recur (inc n)
+             (into #{} (mapcat #(->> (potential-steps %)
+                                     (filter in-bounds?)
+                                     (filter (comp not visited))
+                                     (filter (comp not walls)))
+                               q))
+             (union visited q)))))
+
+;; part 2
+(->> input
+     (map-indexed vector)
+     (drop 2933)
+     first
+     second
+     (str/join ","))