Euler problem 14.1.1

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(defun range (max &key (min 0) (step 1))
  (loop :for n :from min :below max :by step
        collect n))

(defun col (n c)
  (cond ((= n 1) c)     
        ((evenp n) (col (/ n 2) (1+ c)))
        ('t (col (1+ (* 3 n)) (1+ c)))))

(defun max-item (lst)
  (loop :for item :in lst
        :maximize item))

(defun e14 ()
  (let* ((c-lst
           (mapcar #'(lambda (x)
                       (col x 1))
                   (range 1000001 :min 1)))
         (max-len
           (max-item c-lst))
         (max-index
           (1+ (position max-len c-lst))))    
    (list max-index max-len)))

(time (e14))

;; Evaluation took:
;; 1.084 seconds of real time
  
;; (837799 525)

— Me@2023-07-03 12:33:40 AM

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2023.07.03 Monday (c) All rights reserved by ACHK