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我今天在scheme中写了以下代码，但是评估错误。请不要告诉我我编程很烂，我知道这是一个经典的递归问题，但我遇到了麻烦： 

(define (towers-of-hanoi n source temp dest)
 (if (= n 1)
  (begin (display "Move the disk from ")
         (display source) 
         (display " to " )
         (display dest)
         (newline))
 (begin (towers-of-hanoi (- n 1) source temp dest)
        (display "Move the disk from ") 
        (display source)
        (display " to ")
        (display dest)
        (newline)
  (towers-of-hanoi(- n 1) temp source dest))))

我希望代码能够工作，但当我调试它时，我只会让自己更加困惑。谁能帮我？

4

1 回答 1

4

在您的代码中，最后一次递归调用似乎是错误的，并且过程参数的顺序存在问题。试试这个：

(define (towers-of-hanoi n source dest temp)
  (if (= n 1)
      (begin 
        (display "Move the disk from ")
        (display source) 
        (display " to " )
        (display dest)
        (newline))
      (begin 
        (towers-of-hanoi (- n 1) source temp dest)
        (display "Move the disk from ") 
        (display source)
        (display " to ")
        (display dest)
        (newline)
        (towers-of-hanoi (- n 1) temp dest source))))

我注意到您一直在问标记为的问题racket，对于 Racket，这是相同代码的更惯用和更短的版本：

(define (towers-of-hanoi n source dest temp)
  (cond [(= n 1)
         (printf "Move the disk from ~a to ~a~n" source dest)]
        [else
         (towers-of-hanoi (sub1 n) source temp dest)
         (printf "Move the disk from ~a to ~a~n" source dest)
         (towers-of-hanoi (sub1 n) temp dest source)]))

无论哪种方式，它都按预期工作：

(towers-of-hanoi 3 "source" "dest" "temp")

Move the disk from source to dest
Move the disk from source to temp
Move the disk from dest to temp
Move the disk from source to dest
Move the disk from temp to source
Move the disk from temp to dest
Move the disk from source to dest
于 2013-12-05T01:27:34.543 回答