SICP:反复用加法来实现乘法 1.17
#lang racket (define (fast-multiplication a b n);a*n (cond ((= n 0) b);n==0 ((even? n) (fast-multiplication (double a) b (halve n)));even? n (else (fast-multiplication a (+ a b) (- n 1)) );else );cond );fast-multiplication it's iteration (define (fast-multiplication-new a n) (cond ((= n 0) 0) ((= n 1) a) ((even? n) (double (fast-multiplication-new a (halve n)))) (else (a + (fast-multiplication-new a (- n 1))) );else );cond );fast-multiplication-new it's recursive (define (double x) (+ x x));double (define (halve x) (/ x 2) );halve (define (even? x) (= (remainder x 2) 0);= );even (fast-multiplication-new 8 0 1) (fast-multiplication-new 8 0 2) (fast-multiplication-new 8 0 3) (fast-multiplication-new 8 0 4) (fast-multiplication-new 8 0 9)
posted on 2015-03-21 14:30 Zachary_wiz 阅读(122) 评论(0) 编辑 收藏 举报