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(ns org.vuxu.aoc2021.day18
(:require [clojure.string :as str]))
(def data
(->> (slurp "day18")
str/split-lines
(map clojure.edn/read-string)))
(defn add-leftmost [n t]
(if (number? t)
(+ n t)
[(add-leftmost n (first t)) (second t)]))
(defn add-rightmost [n t]
(if (number? t)
(+ n t)
[(first t) (add-rightmost n (second t))]))
(defn explode2 [depth t]
(if (number? t)
nil
(let [[l r] t]
(if (= depth 4)
[0 l r]
(if-let [[l' ln rn] (explode2 (inc depth) l)]
[[l' (add-leftmost rn r)] ln 0]
(if-let [[r' ln rn] (explode2 (inc depth) r)]
[[(add-rightmost ln l) r'] 0 rn]))))))
(defn explode [t]
(first (explode2 0 t)))
(defn split [t]
(if (number? t)
(if (>= t 10)
[(long (Math/floor (/ t 2)))
(long (Math/ceil (/ t 2)))])
(let [[l r] t]
(if-let [l' (split l)]
[l' r]
(if-let [r' (split r)]
[l r'])))))
(defn reduc [t]
(if-let [t' (explode t)]
(recur t')
(if-let [t' (split t)]
(recur t')
t)))
(defn add [x y]
(reduc (conj [x] y)))
(defn mag [t]
(if (number? t)
t
(+ (* 3 (mag (first t)))
(* 2 (mag (second t))))))
(def part1
(mag (reduce add data)))
;; => 4173
(def part2
(apply max
(for [x data
y data
:when (not= x y)]
(mag (add x y)))))
;; => 4706
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