advent-of-code-2025-day1-clj

(ns advent.core
  (:require [clojure.java.io :as io]))

(defn read-input []
  (with-open [rdr (io/reader "input01.txt")]
    (into [] (line-seq rdr))))

(defn parsed-rotations [rotations]
  (mapv (fn [r]
          (let [n (Integer/parseInt (subs r 1))]
            (case (first r)
              \L (- n)
              \R n)))
        rotations))

;; PART1
(second
 (reduce (fn [[position counter] r]
           (let [position' (mod (+ position r) 100)]
             (if (zero? position')
               [position' (inc counter)]
               [position' counter])))
         [50 0]
         (parsed-rotations (read-input "input01.txt"))))

;; PART2
(second
 (reduce (fn [[position counter] r]
           (let [position' (mod (+ position r) 100)
                 turns     (quot (abs r) 100)
                 counter'  (+ counter turns)]
             (if (or (zero? position')
                     (and (not (zero? position)) (neg? r) (> position' position))
                     (and (not (zero? position)) (pos? r) (< position' position)))
               [position' (inc counter')]
               [position' counter'])))
         [50 0]
         (parsed-rotations (read-input "input01.txt"))))