(defun pick (index bag)
  (let* ((range (car bag))
         (beg (car range))
         (end (cdr range))
         (last (- end beg)))
    (if (<= index last)
        (let ((n (+ beg index)))
          (cons n
                (cond
                 ((= last 0)
                  (rest bag))
                 ((= index 0)
                  (cons `(,(1+ beg) . ,end) (rest bag)))
                 ((= index last)
                  (cons `(,beg . ,(- end 1)) (rest bag)))
                 (t
                  (concatenate 'list
                               `((,beg . ,(- n 1))
                                 (,(1+ n) . ,end))
                               (rest bag))))))
      (let* ((rec     (pick (- index last 1) (rest bag)))
             (n       (car rec))
             (new-bag (cdr rec)))
        (cons n (cons range new-bag))))))

(defun generate (count limit)
  (let ((bag `((1 . ,limit)))
        (result nil)
        n pick-result)
    (dotimes (i count)
      (setq pick-result (pick (random (- limit i)) bag))
      (setq n   (car pick-result))
      (setq bag (cdr pick-result))
      (setq result (cons n result)))
    result))