path: root/day03.lisp

(defun input-lines (f)
  (with-open-file (s f)
    (loop for line = (read-line s nil 'eof)
          until (eq line 'eof)
          collect line)))

(defun is-symbol (s i)
  (and (>= i 0)
       (<  i (length s))
       (let ((c (aref s i)))
         (and (not (digit-char-p c))
              (not (equal #\. c))))))

(defun has-symbol (s j k)
  (and s
       (loop for i from j upto k
             if (is-symbol s i)
               return t)))

(defun is-valid-number (prv cur nxt j k)
  (or (is-symbol  cur (1- j))
      (is-symbol  cur k)
      (has-symbol prv (1- j) k)
      (has-symbol nxt (1- j) k)))

(defun sum-valid-numbers-line (prv cur nxt &key (start 0) (acc 0))
  (if (= start (length cur))
      acc
      (multiple-value-bind (n end)
          (parse-integer cur :start start :junk-allowed t)
        (if (and n (digit-char-p (aref cur start)))
            (if (is-valid-number prv cur nxt start end)
                (sum-valid-numbers-line prv cur nxt :start end :acc (+ acc n))
                (sum-valid-numbers-line prv cur nxt :start end :acc acc))
            (sum-valid-numbers-line prv cur nxt :start (1+ start) :acc acc)))))

(defun sum-valid-numbers (rem &key prv (acc 0))
  (if rem
      (sum-valid-numbers (cdr rem)
                         :prv (car rem)
                         :acc (+ acc (sum-valid-numbers-line prv (car rem) (cadr rem))))
      acc))

(defun solve1(f)
  (let ((lines (input-lines f)))
    (sum-valid-numbers lines)))

(defstruct mynumber
  num
  loweri
  lowerj
  upperi
  upperj)

(defstruct mysymbol
  symb
  i
  j)

(defun collect-numbers (lines)
  (labels ((collect-numbers-line (line i start acc)
             (if (< start (length line))
                 (if (digit-char-p (aref line start))
                     (multiple-value-bind (n end)
                         (parse-integer line :start start :junk-allowed t)
                       (collect-numbers-line line i end (cons (make-mynumber :num n
                                                                             :loweri (1- i)
                                                                             :lowerj (1- start)
                                                                             :upperi (1+ i)
                                                                             :upperj end)
                                                              acc)))
                     (collect-numbers-line line i (1+ start) acc))
                 acc))
           (collect-numbers-rec (lines i acc)
             (if lines
                 (collect-numbers-rec (cdr lines)
                                      (1+ i)
                                      (collect-numbers-line (car lines) i 0 acc))
                 acc)))
    (collect-numbers-rec lines 0 ())))

(defun has-adjacent-symbol (gear numbers)
  (loop for number in numbers
        if (is-adjacent number gear)
          collect (mynumber-num number)))


(defun collect-gears (lines)
  (loop for i = 0 then (1+ i)
        for line in lines
        append (loop for j = 0 then (1+ j)
                     for c across line
                     if (equal #\* c)
                       collect (make-mysymbol :symb c :i i :j j))))

(defun is-adjacent (number symbol)
  (and (>= (mysymbol-i symbol) (mynumber-loweri number))
       (<= (mysymbol-i symbol) (mynumber-upperi number))
       (>= (mysymbol-j symbol) (mynumber-lowerj number))
       (<= (mysymbol-j symbol) (mynumber-upperj number))))

(defun find-adjacent-numbers (gear numbers)
  (loop for number in numbers
        if (is-adjacent number gear)
          collect (mynumber-num number)))

(defun solve2 (f)
  (let ((lines (input-lines f)))
    (let ((numbers (collect-numbers lines))
          (gears (collect-gears lines)))
      (loop for gear in gears
            as nums = (find-adjacent-numbers gear numbers)
            if (= (length nums) 2)
              sum (* (car nums) (cadr nums))))))

(print (solve1 "data/03/example.txt")) ;; 4361
(print (solve1 "data/03/input.txt"))   ;; 553079
(print (solve2 "data/03/example.txt")) ;; 467835
(print (solve2 "data/03/input.txt"))   ;; 84363105