2024, day 15

Author: FelipeCortez

2024/15.clj

@@ -0,0 +1,124 @@
+(require '[clojure.string :as str]
+ '[clojure.set :as set])
+
+(def lines (str/split-lines (slurp "2024/15.sample2.in")))
+(def the-map (pop (pop lines)))
+(def moves (peek lines))
+
+(def pos->entity
+ (into {}
+ (for [i (range (count the-map))
+ j (range (count (first the-map)))
+ :let [entity (get-in the-map [i j])]
+ :when (#{\# \@ \O} entity)]
+ (if (= entity \@) (do (def initial-position [i j]) nil)
+ [[i j] entity]))))
+
+(def direction->delta {\< [0 -1], \> [0 1], \^ [-1 0], \v [1 0]})
+(defn p+ [p1 p2] (mapv + p1 p2))
+
+(defn debug [[position pos->entity]]
+ (doseq [i (range (count the-map))
+ j (range (count (first the-map)))]
+ (when (= j 0) (println))
+ (if (= [i j] position)
+ (print \@)
+ (print (or (get pos->entity [i j]) ".")))))
+
+(defn move-and-push [[position pos->entity] direction]
+ ;; (debug [position pos->entity])
+ (let [delta (direction->delta direction)]
+ (loop [looking-at (p+ position delta), seen-box false]
+ (case (get pos->entity looking-at)
+ \O (recur (p+ looking-at delta) true)
+ \# [position pos->entity]
+ [(p+ position delta)
+ (if seen-box
+ (-> pos->entity
+ (dissoc (p+ position delta))
+ (assoc looking-at \O))
+ pos->entity)]))))
+
+(defn gps-sum [[_ pos->entity]]
+ (reduce + (keep (fn [[[i j] c]] (when (= c \O) (+ (* 100 i) j))) pos->entity)))
+
+(gps-sum (reduce move-and-push [initial-position pos->entity] moves))
+
+(defn box-at [boxes [i j]] (or (boxes [i j]) (boxes [i (dec j)])))
+
+(let [*walls (transient #{}), *boxes (transient #{})]
+ (doseq [i (range (count the-map))
+ j (range (count (first the-map)))
+ :let [entity (get-in the-map [i j])]
+ :when (#{\# \@ \O} entity)]
+ (case entity
+ \O (conj! *boxes [i (* j 2)])
+ \# (-> *walls
+ (conj! [i (* j 2)])
+ (conj! [i (inc (* j 2))]))
+ \@ (def initial-position [i (* j 2)])))
+ (def walls (persistent! *walls))
+ (def boxes (persistent! *boxes)))
+
+(defn debug' [[position boxes]]
+ (doseq [i (range (count the-map))
+ j (range (* (count (first the-map)) 2))]
+ (when (= j 0) (println))
+ (cond
+ (= [i j] (box-at boxes [i j]))
+ (print \[)
+
+ (= [i (dec j)] (box-at boxes [i j]))
+ (print \])
+
+ (walls [i j])
+ (print "#")
+
+ (= [i j] position)
+ (print "@")
+
+ :else
+ (print " "))))
+
+(defn move-and-push' [[position boxes] direction]
+ (debug' [position boxes])
+ (let [delta (direction->delta direction)
+ front (p+ position delta)]
+ (loop [positions-to-check #{front}
+ boxes-seen #{}
+ visited #{}]
+ (let [checking-position (first positions-to-check)
+ box-at-position (some->> checking-position (box-at boxes))
+ visit-unvisited
+ (fn [positions-to-check position]
+ (if ((conj visited checking-position) position)
+ positions-to-check
+ (conj positions-to-check position)))]
+ (cond
+ (nil? checking-position)
+ [front
+ (-> boxes
+ (set/difference boxes-seen)
+ (into (map (partial p+ delta) boxes-seen)))]
+
+ (contains? walls checking-position)
+ [position boxes]
+
+ box-at-position
+ (recur (-> positions-to-check
+ (disj checking-position)
+ (visit-unvisited box-at-position)
+ (visit-unvisited (p+ [0 1] box-at-position))
+ (visit-unvisited (p+ delta checking-position)))
+ (cond-> boxes-seen box-at-position (conj box-at-position))
+ (conj visited checking-position))
+
+ :else
+ (recur (disj positions-to-check checking-position)
+ boxes-seen
+ (conj visited checking-position)))))))
+
+(defn gps-sum' [[_ boxes]]
+ (reduce + (map (fn [[i j]] (+ (* 100 i) j)) boxes)))
+
+(gps-sum' (reduce move-and-push' [initial-position boxes] moves))