Sticks

;; See https://programmingpraxis.com/2016/10/07/sticks/

(defun stick (s)
  (setf s (sort s #'<))
  (let ((cost 0) (the-sum 0))
    (do ((x (pop s) (or (null s) (pop s))))
    ((null s) cost)
      (setf the-sum (+ x (car s))
        cost (+ cost the-sum)
        s (insert-sorted the-sum (cdr s))))))

(defun insert-sorted (obj lst)
  (if (null lst)
      (cons obj nil)
      (if (< obj (car lst))
      (cons obj lst)
      (cons (car lst) (insert-sorted obj (cdr lst))))))