tripo.lisp

(defun weak-tripo (n)
  (case n 
    (0 0) 
    (1 0) 
    (2 1)
    (t (+ (weak-tripo (- n 1))
	  (weak-tripo (- n 2))
	  (weak-tripo (- n 3))))))

(let ((table (make-hash-table)))
  (defun super-tripo (n)
    (or (gethash n table)
	(setf (gethash n table)
	      (case n 
		(0 0) 
		(1 0) 
		(2 1)
		(t (+ (super-tripo (- n 1))
		      (super-tripo (- n 2))
		      (super-tripo (- n 3)))))))))


(time (weak-tripo 35)) ; 10 sec
(time (super-tripo 1000)) ; 0 sec