day10.clj

README.md

@@ -46,7 +46,7 @@ Day 00: Helper file                           | [aoc.clj](clojure/aoc.clj)     |
 [Day 07](http://adventofcode.com/2023/day/7)  | [day07.clj](clojure/day07.clj) | Changing card representation is the real MVP.
 [Day 08](http://adventofcode.com/2023/day/8)  | [day08.clj](clojure/day08.clj) | Underwhelming to see _that_ to be solution for part 2.
 [Day 09](http://adventofcode.com/2023/day/9)  | [day09.clj](clojure/day09.clj) | .esreveR
-<!-- [Day 10](http://adventofcode.com/2023/day/10) | [day10.clj](clojure/day10.clj) | -->
+[Day 10](http://adventofcode.com/2023/day/10) | [day10.clj](clojure/day10.clj) | No BFS needed.
 <!-- [Day 11](http://adventofcode.com/2023/day/11) | [day11.clj](clojure/day11.clj) | -->
 <!-- [Day 12](http://adventofcode.com/2023/day/12) | [day12.clj](clojure/day12.clj) | -->
 <!-- [Day 13](http://adventofcode.com/2023/day/13) | [day13.clj](clojure/day13.clj) | -->

clojure/day10.clj

@@ -0,0 +1,56 @@
+(ns day10
+  (:require aoc))
+
+
+(defn find-start [sketch]
+  (key (first (aoc/grid->points sketch #(= % \S)))))
+
+(defn delta [[x y] [px py]]
+  [(- x px) (- y py)])
+
+(defn traverse [sketch start]
+  (loop [[x y :as curr] (aoc/pt+ start [0 1])
+         prev start
+         seen #{}
+         verticals {}]
+    (let [seen' (conj seen curr)
+          [dx dy] (delta curr prev)]
+      (case ((sketch y) x)
+        \S {:pipes seen'
+            :verts verticals}
+        \J (recur (if (zero? dy) [x (dec y)] [(dec x) y])
+                  curr seen' (update verticals y conj x))
+        \L (recur (if (zero? dy) [x (dec y)] [(inc x) y])
+                  curr seen' (update verticals y conj x))
+        \7 (recur (if (zero? dy) [x (inc y)] [(dec x) y])
+                  curr seen' verticals)
+        \F (recur (if (zero? dy) [x (inc y)] [(inc x) y])
+                  curr seen' verticals)
+        \| (recur [(+ x dx) (+ y dy)]
+                  curr seen' (update verticals y conj x))
+        \- (recur [(+ x dx) (+ y dy)]
+                  curr seen' verticals)))))
+
+(defn enclosed [seen verticals h w]
+  (for [y (range h)
+        :let [row-verts (verticals y)]
+        :when row-verts
+        :let [min-vert (apply min row-verts)
+              max-vert (apply max row-verts)]
+        x (range w)
+        :when (and (< min-vert x max-vert)
+                   (not (seen [x y]))
+                   (odd? (aoc/count-if #(< % x) row-verts)))]
+    1))
+
+(defn solve [input-file]
+  (let [sketch (aoc/read-input input-file :chars)
+        start (find-start sketch)
+        h (count sketch)
+        w (count (first sketch))
+        {:keys [pipes verts]} (traverse sketch start)]
+    [(/ (count pipes) 2)
+     (count (enclosed pipes verts h w))]))
+
+
+(solve 10)

clojure/tests/solutions_tests.clj

@@ -1,7 +1,7 @@
 (ns solutions-tests
   (:require
    day01 day02 day03 day04 day05
-   day06 day07 day08 day09 ; day10
+   day06 day07 day08 day09 day10
    ; day11 day12 day13 day14 day15
    ; day16 day17 day18 day19 day20
    ; day21 day22 day23 day24 day25
@@ -33,6 +33,7 @@
 (check-day 7 [6440 5905] [253954294 254837398])
 (check-day 8 nil [11567 9858474970153])
 (check-day 9 [114 2] [1581679977 889])
+(check-day 10 [70 8] [6864 349])
 
 
 (let [summary (run-tests)]