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(ns org.vuxu.aoc2021.day21
(:require [clojure.string :as str]))
(def data
(->> (slurp "day21")
str/split-lines
(map (partial re-find #"\d+$"))
(mapv parse-long)))
(def freqs
(frequencies
(for [a [1 2 3]
b [1 2 3]
c [1 2 3]]
(+ a b c))))
(defn move [roll player state]
(let [state
(update-in state [:pos player] #(inc (mod (dec (+ % roll)) 10)))]
(update-in state [:score player] + (get-in state [:pos player]))))
(def state {:pos data
:score [0 0]})
(def part1
(let [game (take-while (fn [state]
(every? #(< % 1000) (:score state)))
(reductions
(fn [state [player val]]
(move val player state))
state
(map vector
(cycle [0 1])
(map (partial apply +)
(partition 3 (cycle (range 1 101)))))))]
(* (* 3 (count game))
(apply min (:score (last game))))))
;; => 713328
(def play
(memoize
(fn [player state]
(cond
(>= (get-in state [:score 0]) 21) [1 0]
(>= (get-in state [:score 1]) 21) [0 1]
:else
(reduce (fn [result [val freq]]
(mapv + result
(mapv (partial * freq)
(play (- 1 player) (move val player state)))))
[0 0]
freqs)))))
(def part2
(apply max (play 0 state)))
;; => 92399285032143
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