快速求幂 sicp练习1.16

(define (even? n)
  (= (remainder n 2) 0))

(define (fast-expt-iter result b n)
  (cond ((= n 0) 1)
        ((= n 1) (* result b))
        ((even? n) (fast-expt-iter result (* b b) (/ n 2)))
        (else(fast-expt-iter (* b result) b (- n 1)))))

(define (fast-expt b n)
  (fast-expt-iter 1 b n) )

(fast-expt 2 0)
(fast-expt 2 1)
(fast-expt 2 5)
(fast-expt 2 6)