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(ns org.vuxu.aoc2021.day04
(:require [clojure.string :as str]))
(let [[draws & cards] (str/split (slurp "day04") #"\n\n")]
(def draws (->> (str/split draws #",")
(map parse-long)))
(def cards (for [card cards]
(->> card
str/split-lines
(map str/trim)
(mapv #(->> (str/split % #" +")
(mapv parse-long)))))))
(defn find-in [number card]
(first (for [[lineno line] (map-indexed vector card)
[rowno cand] (map-indexed vector line)
:when (= cand number)]
[lineno rowno])))
(defn cross [number card]
(if-let [pos (find-in number card)]
(update-in card pos (constantly true))
card))
(defn won? [card]
(when (or (some (partial every? true?) card)
(some (partial every? true?) (apply mapv vector card)))
card))
(defn score [card draw]
(->> card
flatten
(filter number?)
(apply +)
(* draw)))
(def part1
(reduce (fn [cards draw]
(let [new-cards (map (partial cross draw) cards)]
(if-let [winner (some won? new-cards)]
(reduced (score winner draw))
new-cards)))
cards
draws))
;; => 33348
(def part2
(reduce (fn [cards draw]
(let [new-cards (map (partial cross draw) cards)
remaining-cards (filter (complement won?) new-cards)]
(if (empty? remaining-cards) ; assume only one last winner
(reduced (score (first new-cards) draw))
remaining-cards)))
cards
draws))
;; => 8112
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