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it was math all along....

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This commit is contained in:
Adam Jeniski 2025-08-29 11:38:14 -09:00
parent f60fc29a23
commit 125891900b
1 changed files with 31 additions and 45 deletions
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76
2024/src/day13.clj
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@ -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 +)))