re: AoC Day 2: Inventory Management System VIEW POST

re: Clojure (inefficient part 2) Part 1: (->> (utils/read-file (str utils/resources-path "day2.txt")) (map frequencies) (map vals...

I like the threaded use of update here in part 1 - my method used a transient map and returned a persistent copy at the end:

(ns aoc.aoc2)

(defn reduce-twos-threes
  "check the given frequency map n for twos or threes matches, and update
   the memo map to indicate if the string has a match. Used for a reducer."
  [memo n]
  (let [t-memo (transient memo)]
    (if (some (fn [[k v]] (= v 2)) n) 
      (assoc! t-memo :twos (inc (:twos t-memo))))
    (if (some (fn [[k v]] (= v 3)) n) 
      (assoc! t-memo :threes (inc (:threes t-memo))))
    (persistent! t-memo)))

(defn checksum [input]
  (let [sum-maps (map frequencies input)
        twos-threes (reduce reduce-twos-threes {:twos 0 :threes 0} sum-maps)]
    (* (:twos twos-threes) (:threes twos-threes))))
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