day13.el

;; -*- lexical-binding: t -*-

(defstruct scanner
  (depth 0)
  (range 0))

(defun score (scanner &optional delay)
  (unless delay (setf delay 0))
  (if (= 0 (mod (+ (scanner-depth scanner) delay)
                (* 2 (1- (scanner-range scanner)))))
      (* (scanner-depth scanner)
         (scanner-range scanner))
    0))

(defun hits (scanner &optional delay)
  (unless delay (setf delay 0))
  (if (= 0 (mod (+ (scanner-depth scanner) delay)
                (* 2 (1- (scanner-range scanner)))))
      1
    0))

(defun build-scanner (s)
  (let* ((tokens (split-string s ": " t))
         (numbers (mapcar #'string-to-number tokens)))
    (make-scanner :depth (first numbers)
                  :range (second numbers))))

(defun get-scanners (input)
  (let ((lines (split-string input "\n" t)))
    (mapcar #'build-scanner lines)))

(defun get-score (input &optional delay)
  (apply #'+ (mapcar (lambda (s) (score s delay)) (get-scanners input))))

(defun get-hits (input &optional delay)
  (apply #'+ (mapcar (lambda (s) (hits s delay)) (get-scanners input))))

(let (result)
  (dotimes (i 15)
    (push (get-hits input i) result))
  (reverse result))

(setf input
      (concat
       "0: 3\n"
       "1: 2\n"
       "4: 4\n"
       "6: 4\n"))