递归和线性迭代

;递归
(defun my-fib (x)
  (cond ((= x 0) 0)
    ((= x 1) 1)
    (t (+ (my-fib (- x 1)) (my-fib (- x 2))))))
(defun my-fib-iter (a b count)
  ;(format t "a:~a   and   b:~a  and   count:~a ~%" a b count)
  (cond ((= count 0) b)
    ((= count 1) a)
    (t (my-fib-iter (+ a b) a (decf count)))))
;线性迭代
(defun my-fib-1 (n)
  (my-fib-iter 1 0 n))