From 4d1b77064fd98dae683042acd8e49499fd33c324 Mon Sep 17 00:00:00 2001
From: WillFlame <flameyanai@gmail.com>
Date: Sat, 23 Dec 2023 01:43:23 -0500
Subject: [PATCH] Add 2023 day 23

---
 2023/day23.clj | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 2023/day23.clj

diff --git a/2023/day23.clj b/2023/day23.clj
new file mode 100644
index 0000000..d0c446b
--- /dev/null
+++ b/2023/day23.clj
@@ -0,0 +1,72 @@
+(ns clojure-aoc.core (:gen-class)
+  (:require [clojure-aoc.tools :as tools]
+    [clojure-aoc.grids :as grids]
+    clojure.string))
+
+(def input (-> (slurp "input.txt") (clojure.string/split #"\n")))
+
+(defn longest-path [grid start end]
+  (loop [to-visit [[start #{start} 0]] curr-max 0]
+    (if-let [[curr-loc visited path-len] (peek to-visit)]
+      (if (= curr-loc end)
+        (recur (pop to-visit) (max curr-max path-len))
+        (let [char (grids/at grid curr-loc)
+              neighbours (cond
+                           (= char \.) (grids/neighbours grid curr-loc)
+                           (= char \v) [(map + [0 1] curr-loc)]
+                           (= char \>) [(map + [1 0] curr-loc)])
+              valid? #(and (not= (grids/at grid %) \#) (not (contains? visited %)))
+              valid-neighbours (filterv valid? neighbours)
+              new-visits (map #(vector % (conj visited %) (inc path-len)) valid-neighbours)]
+          (recur (into (pop to-visit) new-visits) curr-max)))
+      curr-max)))
+
+(def part1
+  (let [grid (map seq input)
+        start [(tools/find-index #(= \. %) (first grid)) 0]
+        end [(tools/find-index #(= \. %) (last grid)) (dec (count grid))]]
+    (longest-path grid start end)))
+
+(defn find-intersections [grid]
+  (for [y (range 0 (count grid))
+        x (range 0 (count (nth grid y)))
+        :when (let [neighbours (grids/neighbours grid [x y])]
+                (and (= \. (grids/at grid [x y]))
+                  (> (count (filter #(contains? #{\> \v} (grids/at grid %)) neighbours)) 1)))]
+    [x y]))
+
+(defn find-connections [grid node nodes]
+  (loop [to-visit [[node 0]] visited #{node} connections []]
+    (if-let [[curr-loc path-len] (peek to-visit)]
+      (if (and (not= curr-loc node) (some #(= % curr-loc) nodes))
+        (recur (pop to-visit) (conj visited curr-loc) (conj connections [curr-loc path-len]))
+        (let [neighbours (grids/neighbours grid curr-loc)
+              valid? #(and (not= (grids/at grid %) \#) (not (contains? visited %)))
+              valid-neighbours (filterv valid? neighbours)]
+          (recur (into (pop to-visit) (map #(vector % (inc path-len)) valid-neighbours)) (into visited valid-neighbours) connections)))
+      connections)))
+
+(defn longest-path2 [start end adjacency]
+  (loop [to-visit [[start #{start} 0]] curr-max 0]
+    (if-let [[curr-loc visited path-len] (peek to-visit)]
+      (if (= curr-loc end)
+        (recur (pop to-visit) (max curr-max path-len))
+        (let [neighbours (filter #(not (contains? visited (first %))) (adjacency curr-loc))
+              new-visits (map (fn [[dest len]] (vector dest (conj visited dest) (+ len path-len))) neighbours)]
+          (recur (into (pop to-visit) new-visits) curr-max)))
+      curr-max)))
+
+(def part2
+  (let [grid (map seq input)
+        start [(tools/find-index #(= \. %) (first grid)) 0]
+        end [(tools/find-index #(= \. %) (last grid)) (dec (count grid))]
+        nodes (into (find-intersections grid) [start end])
+        reducer (fn [a curr-node]
+                  (let [connections (find-connections grid curr-node nodes)]
+                    (reduce (fn [acc [dest path-len]]
+                              (assoc-in (assoc-in acc [curr-node dest] path-len) [dest curr-node] path-len)) a connections)))
+        adjacency (reduce reducer {} nodes)]
+    (longest-path2 start end adjacency)))
+
+(defn -main [& args]
+  (println (str part1 " " part2)))