If you want an iterator (rather than a recursive function that returns all relevant combinations), that is easy too: it's just like counting in base n, except that when you overflow you reset the overflowing digit not to zero but to the same (new) value as the preceding digit:

  sub next_iter {
    my($count, $die, $current) = @_;
    return '1' x $count unless $current;
    $current =~ s{
      (?!$die) ((.) $die*) $
    }{
      my $d = $2 + 1;
      $d x length $2
    }ex or return undef;
    return $current;
  }
  ...
  my $cur;
  print $cur while $cur = next_iter(3, 6, $cur);

[download]

Presenting the strings reversed instead allows a slightly cleaner solution with a (rare) useful use of 'cut' - just change the pattern to:

  ( (?>$die*) (.))

[download]
.. and the cut takes up the role of the negative lookahead in ensuring that our incremented digit cannot itself be a match for $die.

Hugo

In reply to Re: unordered sets of N elements by hv
in thread unordered sets of N elements by japhy

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