Re: Recursive loops

[roboticus]

reaper9187:

None of this hand-wavy stuff is helpful at all. If you want to know if recursion is appropriate for your problem, don't look at the structure of your code--look at the structure of your problem.

Going to the basics: If you can express your problem as a solution to a degenerate case or a transformation on a smaller version of the same problem, then you can generally solve it with recursion. (Whether it's the best method of solution is still undetermined, though.).

For a contrived version, suppose you wanted to find out how many vowels are in a string. A stupid recursive solution could be done like so:

my $t='the quick red fox jumped over the lazy brown dog';
print count_vowels($t);

sub count_vowels {
   my $string = shift;

   # Check degenerate case: a single character string.
   if (length($string) == 1) {
      return 1 if $string =~ /a|e|i|o|u/i;
      return 0;
   }

   # Break the problem into two smaller problems:
   my ($part1, $part2) = (substr($string,0,1), substr($string,1) );
   return count_vowels($part1) + count_vowels($part2);
}

Note: Yes, I've oversimplified a bit.

...roboticus

When your only tool is a hammer, all problems look like your thumb.