Submission #2408191

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Source Code Expand

(defun take (l n)
  (if (or (null l) (= n 0))
      '()
      (cons (car l) (take (cdr l) (1- n)))))


(defun far-the-most-dot (list)
  (let* ((l (reverse list))
         (l-size (length list))
         (pos (position #\. l)))
    (when pos
      (- (1- l-size) pos))))

(defun far-the-most-x (list)
  (let* ((l (reverse list))
         (l-size (length list))
         (pos (position #\X l)))
    (when pos
      (- (1- l-size) pos))))

(defun calc-next-pos (list)
  (or (far-the-most-dot list)
      (far-the-most-x list)))


(defun calc-step-positions (list start-pos)
  (if (< (length list) 5)
      '()
      (let* ((l (take (cdr list) 3))
             (next-pos (+ (calc-next-pos l) 1 start-pos)))
        (cons next-pos
              (calc-step-positions (subseq list next-pos) next-pos)))))

(let* ((_ (read))
       (s (concatenate 'list (string-right-trim '(#\Newline) (read-line))))
       (step-positions (calc-step-positions s 0))
       (x-num (count-if (lambda (idx) (equal (nth idx s) #\X)) step-positions)))
  (format 't "~A~%" x-num))

Submission Info

Judge Result