From 125891900bce271a22cfd564b2277358c9b0bc76 Mon Sep 17 00:00:00 2001
From: ajet <ajeniski4@gmail.com>
Date: Fri, 29 Aug 2025 11:38:14 -0900
Subject: [PATCH] it was math all along....

---
 2024/src/day13.clj | 76 +++++++++++++++++++---------------------------
 1 file changed, 31 insertions(+), 45 deletions(-)

diff --git a/2024/src/day13.clj b/2024/src/day13.clj
index f4eb7f6..153a662 100644
--- a/2024/src/day13.clj
+++ b/2024/src/day13.clj
@@ -4,58 +4,44 @@
    [input-manager :refer [get-input-raw]]))
 
 (def input
-  (->> (get-input-raw 13)
+  (->> (get-input-raw 2024 13)
        c/split-on-double-newlines
        (map #(c/get-match-groups #"(\d+)" %))
        (c/mmap first)
        (c/mmap parse-long)
        (map #(map vector [:ax :ay :bx :by :px :py] %))
-       (map #(into {} %))
-       ;
-       ))
-
-(defn push [m k vs]
-  (if (empty? vs)
-    m
-    (update m k #(if (nil? %1)
-                   (set vs)
-                   (into %1 %2))
-            vs)))
+       (map #(into {} %))))
 
 (defn get-cost [{:keys [ax ay bx by px py]}]
-  (loop [costs (sorted-map 0 #{[0 0]})
-         i 0]
-    (let [[cost locs] (first costs)
-          costs' (dissoc costs cost)]
-      (if (or (nil? cost)
-              (> i 1000)
-              (some (fn [[x y]]
-                      (and (= x px)
-                           (= y py)))
-                    locs))
-        costs
-        (recur (-> costs'
-                   (push (+ cost 3)
-                         (->> locs
-                              (map #(-> %
-                                        (update 0 + ax)
-                                        (update 1 + ay)))
-                              (filter (fn [[x y]]
-                                        (and (<= x px)
-                                             (<= y py))))))
-                   (push (+ cost 1)
-                         (->> locs
-                              (map #(-> %
-                                        (update 0 + bx)
-                                        (update 1 + by)))
-                              (filter (fn [[x y]]
-                                        (and (<= x px)
-                                             (<= y py)))))))
-               (inc i))))))
+  ;; systems of equations. had to get out a pen and paper to work out a and b ;P
+  ;; px = ax * a + bx * b
+  ;; py = ay * a + by * b
+  (let [b (/ (- (* ax py)
+                (* ay px))
+             (- (* ax by)
+                (* bx ay)))
+        a (/ (- px (* b bx))
+             ax)]
+    (when (= 0.0
+             (mod a 1.0)
+             (mod b 1.0))
+      (+ (* 3 a) b))))
 
+(comment
 ;; part 1
-(->> input
-     (map get-cost)
-     (filter identity)
-     (reduce +))
+  (->> input
+       (map get-cost)
+       (filter identity)
+       (filter identity)
+       (reduce +)
+       ;
+       )
 
+  (def offset 10000000000000)
+  (->> input
+
+       (map #(update % :px + offset))
+       (map #(update % :py + offset))
+       (map get-cost)
+       (filter identity)
+       (reduce +)))