From cf8beef728ca3ddb4e037016679bce63c37c2c7b Mon Sep 17 00:00:00 2001
From: WillFlame <flameyanai@gmail.com>
Date: Mon, 11 Dec 2023 22:59:15 -0500
Subject: [PATCH] Add 2023 day 10

---
 2023/day10.clj | 119 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 2023/day10.clj

diff --git a/2023/day10.clj b/2023/day10.clj
new file mode 100644
index 0000000..c9bc59b
--- /dev/null
+++ b/2023/day10.clj
@@ -0,0 +1,119 @@
+(ns clojure-aoc.core (:gen-class)
+  (:require [clojure-aoc.tools :as tools]
+    [clojure-aoc.grids :as grids]
+    clojure.set
+    clojure.string))
+
+(def input (-> (slurp "input.txt") (clojure.string/split #"\n")))
+
+(def pipes
+  {\| [:up :down]
+   \- [:left :right]
+   \L [:up :right]
+   \J [:up :left]
+   \7 [:down :left]
+   \F [:down :right]
+   \. []})
+
+(defn find-start [grid]
+  (first (for [y (range (count grid))
+               x (range (count (nth grid y)))
+               :when (= (tools/at grid [x y]) \S)]
+           `(~x ~y))))
+
+
+
+(defn find-neighbours [grid loc]
+  (->> tools/grid-dirs
+    (map (fn [[dir d]] [(map + d loc) dir]))
+    (filter (fn [[new-loc dir]]
+              (and
+                (tools/in-bounds grid new-loc)
+                (let [pipe (tools/at grid new-loc)]
+                  (some #(= % (grids/opposite-dir dir)) (pipes pipe))))))))
+
+(defn traverse [grid [loc dir]]
+  (let [pipe (tools/at grid loc)
+        next-dir (first (filterv #(not= % (grids/opposite-dir dir)) (pipes pipe)))
+        next-loc (mapv + loc (tools/grid-dirs next-dir))]
+    [next-loc next-dir]))
+
+(defn find-loop [grid]
+  (let [start (find-start grid)
+        start-next (first (find-neighbours grid start))]
+    (loop [path [] [loc _ :as curr] start-next]
+      (if (= loc start)
+        (conj path curr)
+        (recur (conj path curr) (traverse grid curr))))))
+
+(def part1
+  (let [grid (map seq input)
+        pipe-loop (tools/debug (find-loop grid))]
+    (quot (count pipe-loop) 2)))
+
+(defn flood
+  "Returns the set of all connected points, given a grid and a seq of walls."
+  [grid initial-loc walls]
+  (loop [to-visit [initial-loc] visited #{}]
+    (if-let [curr (peek to-visit)]
+      (let [neighbours (->> (tools/neighbours grid curr)
+                         (filter (fn [new-loc]
+                                   (and
+                                     (not (some #(contains? % new-loc) [walls visited]))
+                                     (every? #(not= % new-loc) to-visit)))))
+            new-visit (into (pop to-visit) neighbours)
+            new-visited (conj visited (apply list curr))]
+        (recur new-visit new-visited))
+      visited)))
+
+(defn turning-out?
+  "Returns whether the path turns outwards (e.g. enclosing ccw, moving right and encounting a 7 is an outward turn). "
+  [dir pipe cw?]
+  (let [other-dir (first (filterv #(not= % (grids/opposite-dir dir)) (pipes pipe)))]
+    (= (tools/turn dir (if cw? :left :right)) other-dir)))
+
+;; Try to turn right (or left) at every step and dfs on the node to catch all connected squares.
+;; If the path curves outwards, you also need to move forward and dfs on that node (catches edge cases).
+(defn enclosed [grid cw?]
+  (let [pipe-loop (find-loop grid)
+        loop-locs (into #{} (map first pipe-loop))
+        rotate-dir (if cw? :right :left)
+        reducer (fn [visited [loc dir]]
+                  (let [inside (map + loc (tools/grid-dirs (tools/turn dir rotate-dir)))
+                        pipe (tools/at grid loc)
+                        insides (if (and (some #(= % pipe) (seq "7JLF")) (turning-out? dir pipe cw?))
+                                  [inside (map + loc (tools/grid-dirs dir))]
+                                  [inside])
+                        valid-insides (filter #(and
+                                                 (tools/in-bounds grid %)
+                                                 (not (contains? loop-locs %))
+                                                 (not (contains? visited %))) insides)
+                        flooded (map #(flood grid % loop-locs) valid-insides)]
+                    (reduce clojure.set/union visited flooded)))]
+    (reduce reducer #{} pipe-loop)))
+
+(def part2
+  (let [grid (map seq input)]
+    (->> (map #(enclosed grid %) [true false])
+      (filter #(not (contains? % [0 0])))
+      first
+      count)))
+
+
+(defn -main [& args]
+  (str part1 " " part2))
+
+;; I leave this behind as a memory of my alternate solution that died to corners. RIP
+
+; (defn inside [locs grid ind vert?]
+;   (println (str "looking in " ind))
+;   (loop [i 0 in? false total 0]
+;     (if (= i (if vert? (count grid) (count (nth grid ind))))
+;       total
+;       (let [pipe? (contains? locs i)
+;             char (tools/at grid (if vert? [ind i] [i ind]))
+;             new-in? (if (and pipe? (= char (if vert? \- \|))) (not in?) in?)
+;             new-total (if (and (not pipe?) in?) (inc total) total)]
+;         (if (and pipe? (= char (if vert? \- \|))) (println (str "toggle " i)) ())
+;         (if (and (not pipe?) in?) (println i) ())
+;         (recur (inc i) new-in? new-total)))))