将数字转换为数字列表 [英] Convert number to list of digits

问题描述

如何将数字转换为数字列表?

How do I convert a number to a list of digits?

我目前正在做的:

;; (num->list 12345) -> '(1 2 3 4 5)
(define (num->list n)
  (local 
    ((define (num->list n)
       (map (lambda (c)
              (char->num c))
            (string->list (number->string n))))

    (define (char->num c)
      (- (char->integer c) 48)))

    (num->list n)))

但想知道是否有更好的方法.

but would like to know if there's a better way.

推荐答案

这是digits 我的标准序曲的功能:

This is the digits function of my Standard Prelude:

(define (digits n . args)
  (let ((b (if (null? args) 10 (car args))))
    (let loop ((n n) (d '()))
      (if (zero? n) d
          (loop (quotient n b)
                (cons (modulo n b) d))))))

您的函数版本在字符串和数字之间来回切换；我的版本纯粹是算术.我的版本还提供十进制以外的基数.

Your version of the function goes back-and-forth between strings and numbers; my version is purely arithmetic. My version also provides for bases other than decimal.

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