FWIW my solution just limits the range of witnesses: 
        for my $witness (2..int((10**length($i) - 1) / $i)) {
            if ($i_sorted eq join '', sort split //, $i * $witness) {
                if (++$pairs == $count) {
                    ++$qualifying_integers;
                    next I;
                }
            }
        }
        # maximum witness can't be more than i's first digit
        for my $witness (2..substr $i, 0, 1) {
            if (!( $i % $witness ) && $i_sorted eq join '', sort split
+ //, $i / $witness) {
                if (++$pairs == $count) {
                    ++$qualifying_integers;
                    next I;
                }
            }
        }

[download]
and tries to limit the ops executed in the loop body. To take advantage of other witness elimination, you'd unwrap the outer loop and have special code for e.g multiples of 3, but that if a lot of duplication. You'd get a much better speed bump using Inline for at least the "does it have the same digits" check. My go solution is much much faster. But all the conversions from numbers to strings to runes make it a lot longer.

Python was interesting; it lacks the ability to continue an outer loop, so the two inner loop approach needed an additional flag variable. But Python's iterator design made a single inner loop possible, at a slight speed penalty but producing the tersest code.

In reply to Re: Faster (but uglier) PWC 350-2 solutions by ysth
in thread Faster (but uglier) PWC 350-2 solutions by Anonymous Monk

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