--- David <[EMAIL PROTECTED]> wrote:
> Mickey Mathieson a écrit :
> > I am new to the group and have noticed a lot of
> questions of
> > recursion.
> > A problem that is suitable for recursion should
> produce a smaller
> > function that if the problem was solved without
> recursion. This has
> > not been the case from the postings that i have
> looked at.
> >
> > I have provided an example of recursion done
> correctly to reverse a
> > string. Notice how short and compact the code is.
> This is the object
> > of recursion - less code at the expense of more
> memory being used.
> >
> > Mickey M.
> > senior software engineer
> > http://www.constructionpartner.com
> >
> >
> > // Reverse String
> > char *RevStr(int count, char *str)
> > {
> > char Value;
> >
> > if (count)
> > {
> > Value = str[count-1];
> > RevStr(count-1, str);
> > }
> >
> > if (count)
> >
> this test has no use, since count did not change
> since the last test
>
> > str[strlen(str) - count] = Value;
> >
> > return(str);
> > }
> >
>
> To made even shorter (and poor efficiency... strlen
> is called far too
> often, hope you newer reverse very long string)
> char *RevStr(int c, char *str) {
> if (c) {
> char Value = str[c-1]; // some C compiler
> could complain about
> inside declaration of Value
> str[ strlen( RevStr( c-1, str ) ) - c] =
> Value; // strlen is
> stable
> }
> return(str);
> }
>
> A simple iterative one could be (IMHO far more
> efficient else there is a
> bug)
>
> char* reverse( char* str ) {
> char* begin = str, *end = str;
> while( *end ) ++end; // go to the end
> while( end > begin ) { // swap begin and end
> until they join
> char c = *--end;
> *end = *begin;
> *begin++ = c;
> }
> return str;
> }
>
> and a C++ one could be (a one line)
> std::reverse( str, str + strlen( str ) );
> > int main(int argc, char* argv[])
> > {
> >
> > char Test[20] = "ABCDEFGHIJK";
> > char Out[20];
> >
> > strcpy(Out,RevStr(strlen(Test), Test));
> >
> >
> > return 0;
> > }
> >
> >
>
> A function like Ackermann could have been a better
> example of
> recursivity efficiency.
>
> When I tought about it, I wonder if this is not a
> fake to hide some
> homework...
>
> Regards,
> David
>
>
// Reverse String
char *RevStr(int count, char *str)
{
if (!count) return(str);
char Value = str[count-1];
RevStr(count-1, str);
str[strlen(str) - count] = Value;
return(str);
}
int main(int argc, char* argv[])
{
char Test[20] = "ABCDEFGHIJK";
char Out[20];
strcpy(Out,RevStr(strlen(Test), Test));
return 0;
}
The problem is about Recursion - not using loops.
Sure I could shorten it more but why to confuse the
people i am trying to explain it too!
Anyone can come up with a loop solution such as you
did. Again this did not answer the question.
Mickey
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