sicp 习题

1 #lang racket
2 (define (fff n)
3   (define (fff-iter a b c n)
4     (if (= n 0)
5         a
6         (fff-iter b c (+ (* 3 a)(* 2 b) c) (- n 1))))
7   (fff-iter 0 1 2 n))

#lang racket
(define (fff n)
  (if (< n 3)
      n
      (+ (fff (- n 1))
         (* 2 (fff (- n 2)))
         (* 3 (fff (- n 3))))))

#lang racket
(define (pascal row col)
  (cond ((< row col) (error "error"))
        ((or (= col 0) (= col row)) 1)
        (else (+ (pascal (- row 1)  col)
                 (pascal (- row 1) (- col 1))))))