(ql:quickload "str")

;; (defun file-get-contents (filename)
;;   (with-open-file (stream filename)
;;     (let ((contents (make-string
;;                      (file-length stream))))
;;       (read-sequence contents stream)
;;       contents)))

(defun file-get-lines (filename)
  (with-open-file (stream filename)
    (loop :for line = (read-line stream nil)
          :while line
          :collect line)))

;; (defun string-to-list (the-string)
;;   (loop :for char :across the-string
;;         :collect char))

;; (defun char-to-integer-list (char-list)
;;   (mapcar #'digit-char-p char-list))

(defun path-add-item (x yys zzs)
  (let* ((y (car yys))
         (ys (cdr yys))
         (z (car zzs))
         (zs (cdr zzs))
         (m (if (> y z) y z))
         (ms (if (> y z) ys zs)))
    (cons (+ x m) (cons x ms))))

(defmacro zipWith3 (f xs ys zs)
  `(mapcar ,f ,xs ,ys ,zs))

(defun path-add-item-zip (acc xs)
  (zipWith3 #'path-add-item xs acc (cdr acc)))

(defun foldl (f acc xs)
  (if (not xs)
      acc
      (foldl f (funcall f acc (car xs)) (cdr xs))))

(defun string-split (x)
  (str:split #\space x))

(defun map-parse-integer (xs)
  (mapcar #'parse-integer xs))

(defmacro map-string-split (xs)
  `(mapcar #'string-split ,xs))

(defmacro head (xs)
  `(car ,xs))

(defmacro tail (xs)
  `(cdr ,xs))

(defun pair-double (x)
  (list x x))

(defun e18 ()
  (let* ((string-lines (file-get-lines #P"n.txt"))
         (string-lists (map-string-split string-lines))
         (number-tower (mapcar #'map-parse-integer
                               string-lists))
         (r-tower (reverse number-tower))
         (acc (mapcar #'pair-double (head r-tower))))
    
    (foldl #'path-add-item-zip acc (tail r-tower))))

CL-USER> (e18)
((1074 75 64 82 87 82 75 73 28 83 32 91 78 58 73 93))
CL-USER> 

— Me@2023-12-20 07:32:00 PM

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2023.12.21 Thursday (c) All rights reserved by ACHK