src/2021/days/day-04.lisp @ cec05589a84c

(advent:defpackage* :advent/2021/04)
(in-package :advent/2021/04)

;; Cells ----------------------------------------------------------------------
(defun cell (num) (cons num nil))
(defun num (cell) (car cell))
(defun markedp (cell) (cdr cell))
(defun unmarkedp (cell) (not (markedp cell)))
(defun mark (cell) (setf (cdr cell) t))


;; Input ----------------------------------------------------------------------
(defun read-bingo-numbers (stream)
  (read-numbers-from-string (read-line stream)))

(defun read-board (&optional (stream *standard-input*) (eof-error-p t) eof-value)
  (peek-char t stream nil)
  (with-eof-handled (stream eof-error-p eof-value)
    (do-array (v (make-array '(5 5)))
      (setf v (cell (parse-integer (read-word stream)))))))

(defun parse (stream)
  (values (read-bingo-numbers stream)
          (read-and-collect stream #'read-board)))


;; Boards ---------------------------------------------------------------------
(defun copy-board (board)
  (do-array (cell (alexandria:copy-array board))
    (setf cell (cons (car cell) (cdr cell)))))

(defun print-board (board)
  (print-2d-array board :printer (lambda (cell)
                                   (when (markedp cell) (green) (bold))
                                   (format t "~3D" (num cell))
                                   (when (markedp cell) (reset)))))

(defun print-boards (boards &optional heading)
  (when heading (write-line heading))
  (dolist (board boards)
    (print-board board)
    (terpri)))


;; Playing --------------------------------------------------------------------
(defun mark-number-on-board (n board)
  (do-array (cell board)
    (when (= n (num cell))
      (return (mark cell)))))

(defun mark-number-on-boards (n boards)
  (dolist (board boards)
    (mark-number-on-board n board)))

(defun winning-row-p (board row)
  (iterate (for col :below 5) (always (markedp (aref board row col)))))

(defun winning-col-p (board col)
  (iterate (for row :below 5) (always (markedp (aref board row col)))))

(defun winning-board-p (board)
  (or (iterate (for row :below 5) (thereis (winning-row-p board row)))
      (iterate (for col :below 5) (thereis (winning-col-p board col)))))

(defun play-first (numbers boards)
  (iterate
    (with boards = (mapcar #'copy-board boards))
    (for n :in numbers)
    (mark-number-on-boards n boards)
    (dolist (board boards)
      (when (winning-board-p board)
        (return-from play-first (values n board))))))

(defun play-last (numbers boards)
  (iterate
    (with boards = (mapcar #'copy-board boards))
    (for n :in numbers)
    (mark-number-on-boards n boards)
    (if (null (rest boards))
      (when (winning-board-p (first boards)) ;; Run last board to completion.
        (return-from play-last (values n (first boards))))
      (setf boards (delete-if #'winning-board-p boards))))) ;; Still pruning boards.

(defun unmarked-sum (board)
  (iterate (for cell :across-flat-array board)
           (when (unmarkedp cell)
             (summing (num cell)))))

(defun score (last-number board)
  (* last-number (unmarked-sum board)))

;; Main -----------------------------------------------------------------------
(define-problem (2021 4) (data) (49860 24628)
  (multiple-value-bind (numbers boards) (parse data)
    (values
      (multiple-value-call #'score (play-first numbers boards))
      (multiple-value-call #'score (play-last numbers boards)))))


#; Scratch --------------------------------------------------------------------