day 8

deps.edn

@@ -1,3 +1,4 @@
 {:paths ["src" "cookies"]
  :deps {org.clojure/clojure {:mvn/version "1.12.0"}
-        clj-http/clj-http {:mvn/version "3.13.0"}}}
+        clj-http/clj-http {:mvn/version "3.13.0"}
+        org.clojure/math.combinatorics {:mvn/version "0.3.0"}}}

src/day8.clj

@@ -0,0 +1,80 @@
+(ns day8
+  (:require [mapped-area]
+            [helpers :refer [get-input]]
+            [clojure.math.combinatorics :refer [combinations]]))
+
+(def test-city
+"............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............")
+
+(def test-city2
+"..........
+..........
+..........
+....a.....
+........a.
+.....a....
+..........
+..........
+..........
+..........")
+
+(defn antinodes [a [[x1 y1] [x2 y2]]]
+  (let [xd (- x1 x2)
+        yd (- y1 y2)
+        an1 [(+ x1 xd) (+ y1 yd)]
+        an2 [(- x2 xd) (- y2 yd)]]
+    (filter (partial mapped-area/mapped? a) [an1 an2])))
+
+(defn antennas [a]
+  (reduce
+   (fn [m [coord value]]
+     (if (= value \.)
+       m
+       (update m value #(conj % coord))))
+   {}
+   (mapped-area/mapped-area-indexed-seq a)))
+
+(defn antenna-pairs [a]
+  (mapcat (fn [[_ a]] (combinations a 2)) (antennas a)))
+
+(defn find-antinodes [m a-fn]
+  (let [a (mapped-area/read-mapped-area m)]
+    (->> (antenna-pairs a)
+         (mapcat #(a-fn a (vec %))))))
+
+(println "Number of antinodes:"
+         (->
+          (get-input 8)
+          (find-antinodes antinodes)
+          set
+          count))
+
+(defn antinodes-resonant [a [[x1 y1] [x2 y2]]]
+  (let [xd (- x1 x2)
+        yd (- y1 y2)
+        nodes-fn
+        (fn [x y nodes op]
+          (if (not (mapped-area/mapped? a x y))
+            nodes
+            (recur (op x xd) (op y yd) (conj nodes [x y]) op)))]
+    (concat
+     (nodes-fn x1 y1 [] +)
+     (nodes-fn x2 y2 [] -))))
+
+(println "Number of antinodes:"
+         (->
+          (get-input 8)
+          (find-antinodes antinodes-resonant)
+          set
+          count))

src/mapped_area.clj

@@ -71,3 +71,8 @@ ijkl")
 (test #'h)
 (test #'w)
 (test #'mapped?)
+
+(defn mapped-area-indexed-seq [a]
+  (for [x (range (w a))
+        y (range (h a))]
+    (vector [x y] (get-in a [x y]))))