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Re^5: Golf: Tree searching

by tadman (Prior)
on Apr 20, 2001 at 08:36 UTC ( #74078=note: print w/replies, xml ) Need Help??

in reply to Re (tilly) 4: Golf: Tree searching
in thread Golf: Tree searching

Inspirationally shameless, and a great demonstration of the power of 'and' versus '&&', something that I hadn't fully understood. Until now. I have to say, at first it looks like a drop-in alternative to the presumably scary C-style double-ampersands (as in, an artifact of the use English movement), but when you get right down to it, it binds much more loosely, enhancing its utility vastly.

In the spirit of shameless borrowing, switching to 'pop' and using 'and' nets the following: sub f{for($t=pop;$_=(0,l,r)[$$t{d}cmp$_[0]]and$t=$$t{$_};){}$t}
But this is really just converging on the same thing: sub f{for($t=pop;$_=$$t{d}cmp$_[0]and$t=$$t{$_>0?l:r};){}$t}
Which is the same length, and functionally the same due to heavy cross-pollination.

Of course, if the spec had indicated that the two branches were labelled '-1' and '1' instead of 'r' and 'l', that would certainly simplify things a whole lot. Or at least it would save 6 precious characters: sub f{for($t=pop;$_=$$t{d}cmp$_[0]and$t=$$t{$_};){}$t}

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Re (tilly) 6: Golf: Tree searching
by tilly (Archbishop) on Apr 20, 2001 at 15:18 UTC
    A tip. Whenever possible go for the one-line looping constructs. The following two are equivalent logically:
    for(A;B;C){} A;C while B;
    however the second has 3 characters you may be able to drop. So use it. Even if it means using commas etc in C to get it to work, use it. (I am able to drop the 2 spaces.) A technicality, to be sure, but a significant one.

    Also while the binding of and can make it better than &&, if you see it used that way, look for a way to move things around to get the && in somewhere and save a character. Watch:

    sub f { $t=pop;$t=$$t{$c>0?l:r}while$c=$t&&$$t{d}cmp$_[0];$t }
    Not something you would write from scratch, but there you have it...

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[Corion]: hippo: If you have a Unicode-wise Perl then likely some zero-width characters in $x would work. Maybe $x = "\x{200b}" works.
[Corion]: Hmm - no, that outputs 1 for me on 5.14 - perl -wle "my $x = qq(\x{200b}); warn $x; warn length $x"
[hippo]: Smart - I'll give that a go. Thanks.
[hippo]: Ah
[Corion]: But maybe there is some other Unicode string that will be true but have a zero width
[hippo]: For explanation, I've seen this construct in someone else's code (no names, no pack drill) and couldn't think of a situation to trigger it.
[Corion]: You'll have to look somewhere esoteric for that. Maybe some tied variable or special dualvar can also trigger that. But it's certainly not a common occurrence
[Corion]: And on 5.20, the following also outputs no find:perl -wle 'for my $x ("\x{2000}".."\ x{1fffff}") { if( $x && ! length $x ) { warn qq(<$x>); warn length $x; die } }'
[Corion]: (this time on Unix)
[hippo]: Understood. I'll have to go through the code and see if it's doing anything fancy with ties, dual-vars or non-scalars. In the end, it's probably a bug though.

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