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我正在尝试在方案中将两个数字（来自列表）相加，同时保留列表格式。但是，当用于计算的数字加起来大于或等于 10 时，我会得到不想要的结果。例如：

(define (reverse lst)
  (if (null? lst)
      '()
      (append (reverse (cdr lst)) 
          (list (car lst)))))

(define (apa-add lst1 lst2)
  (cond ((null? lst1) lst2)
    ((null? lst2) lst1)
    ((>= (+ (car lst1) (car lst2)) 10) 
     (append (apa-add (cdr lst1) (cdr lst2)) 
         (list (quotient(+ (car lst1) (car lst2)) 10)) 
         (list (modulo (+ (car lst1) (car lst2)) 10))))
        (else 
         (append (apa-add (cdr lst1) (cdr lst2))
         (list (+ (car lst1) (car lst2)))))))

(apa-add (reverse '(4 4 5)) (reverse'(3 5 8)))

返回

'(7 9 1 3)

如何修改我的代码以修复此错误？我想使用一个语句，这样我就可以添加对下一次调用let的评估 ，但我想不出该怎么做。(quotient (+ (car lst1) (car lst2)) 10)(list (+ (car lst1) (car lst2)))

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1 回答 1

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把它变成一个尾调用可以简化一些事情。

(define (apa-add lst1 lst2)
  (let loop ((carry 0) (L1 (reverse lst1)) (L2 (reverse lst2)) (sum '()))
     (cond ((and (null? l1) (null? l2)) 
            (if (zero? carry) sum (cons carry sum)))
           ((null? L1) 
            (loop (quotient (+ carry (car l2)) 10)
                  '() 
                  (cdr L2) 
                  (cons (modulo (+ carry (car l2)) 10) sum)))
           ((null? L2) 
            (loop (quotient (+ carry (car l1)) 10)
                  (cdr l1) 
                  '() 
                  (cons (modulo (+ carry (car l1)) 10) sum)))
           (else  
            (loop (quotient (+ carry (car l1) (car l2)) 10)
                  (cdr l1) 
                  (cdr l2)
                  (cons (modulo (+ carry (car l1) (car l2)) 10) sum))))))              



(apa-add (list 4 4 5) (list 3 5 8))

;Value 4: (8 0 3)

转换为 n 元函数可能不会太难。

(define (apa-add . Lists)
  (define (cdrs-no-null L)
               (cond ((null? L) '())
                     ((null? (cdar l)) (cdrs-no-null (cdr L)))
                     (else (cons (cdar l) (cdrs-no-null (cdr l))))))
    (let loop ((carry 0) (Lists (map reverse Lists)) (sum '()))
          (if (null? Lists)
              (if (zero? carry) sum (cons carry sum))
              (loop (quotient (fold + carry (map car Lists)) 10)
                    (cdrs-no-null Lists)
                    (cons (modulo  (fold + carry (map car Lists)) 10) sum)))))

(apa-add (list 4 4 5) (list 3 5 8) (list 1 0 2 7))

;Value 11: (1 8 3 0)

(apa-add (list 4 4 5) (list 3 5 8))

;Value 12: (8 0 3)
于 2013-10-23T18:28:24.137 回答