do day 16

2023/src/day16.clj

@@ -0,0 +1,78 @@
+(ns day16 (:require [core :refer [get-puzzle-input]]))
+
+(def input (get-puzzle-input 16))
+(def char-map (->> input
+                   (map-indexed (fn [row line]
+                                  (map-indexed (fn [col c]
+                                                 [[row col] c])
+                                               line)))
+                   (apply concat)
+                   (into {})))
+(def N (count input))
+
+(defn next-loc [{dir   :dir
+                 [r c] :loc
+                 :as   arg}]
+  (let [[r' c' :as ans] (condp = dir
+                          :left  [r (dec c)]
+                          :right [r (inc c)]
+                          :up    [(dec r) c]
+                          :down  [(inc r) c])]
+    (when (and (< -1 r' N)
+               (< -1 c' N))
+      (assoc arg :loc ans))))
+
+(defn apply-mirrors [{dir   :dir
+                      loc   :loc
+                      :as   arg}]
+  (cond (and (#{:left :right} dir)
+             (= (char-map loc) \|))
+        (list (assoc arg :dir :up) (assoc arg :dir :down))
+
+        (and (#{:up :down} dir)
+             (= (char-map loc) \-))
+        (list (assoc arg :dir :left) (assoc arg :dir :right))
+
+        (= (char-map loc) \\)
+        (list (assoc arg :dir (condp = dir
+                                :left :up
+                                :right :down
+                                :up :left
+                                :down :right)))
+
+        (= (char-map loc) \/)
+        (list (assoc arg :dir (condp = dir
+                                :left :down
+                                :right :up
+                                :up :right
+                                :down :left)))
+
+        :else (list arg)))
+
+(defn measure-energy [start]
+  (->> (loop [beams [start]
+              visited #{}]
+         (let [beams' (->> (keep next-loc beams)
+                           (map apply-mirrors)
+                           (apply concat)
+                           (filter (complement visited)))]
+           (if (not-empty beams')
+             (recur beams'
+                    (apply conj visited beams'))
+             visited)))
+       (map :loc)
+       distinct
+       count))
+
+;; part 1
+(measure-energy {:dir :right
+                 :loc [0 -1]})
+
+;; part 2
+(->> [(for [c (range N)] {:loc [N c],  :dir :up})
+      (for [c (range N)] {:loc [-1 c], :dir :down})
+      (for [r (range N)] {:loc [r -1], :dir :right})
+      (for [r (range N)] {:loc [r N],  :dir :left})]
+     (apply concat)
+     (map measure-energy)
+     (apply max))