NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/13342

Internet Message Format | 1996-08-05 | 1.6 KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: reversing a string
Date: Sun, 07 Apr 96 10:48:36 GMT
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References: <4k6cjl$[e-mail]>
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In article <4k6cjl$[e-mail]>
           [e-mail] "Leland Newsom" writes:

>I have a challenge from a friend of mine.  He wanted me to reverse a string
>with recursion without using any additional variables or loops.  I got mine
>to work by using exclusive or, but I needed an additional variable.  Can
>someone help with this problem without using the additional variable?

There is a solution although (the one I'm thinking of) won't gain any
prizes for efficiency. I won't give the answer (yet) because this is a
worthwhile problem for getting used to recursion. All you need is a function:


void reverse(char *str)
{
    ...
}

Within that the operations you have available are to swap 2 characters at
the start of the string (you don't know where the end is) using, say, an
exclusive or swap, and to reverse a shorter suffix of the string via a
recursive call. You should aim to get from something like:

    a b c d e f g

to

    g a b c d e f

which can then be completed via a call to reverse(str+1)

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
-----------------------------------------