Fixed:

sub comp {
    my ($f, $s) = @_;
    return -1 if length ($f) != length ($s);

    local $_ = $f ^ $s;
    return -1 unless tr/\x00/1/c == 2;

    my $i = index $_ => "11";
    return -1 unless $i >= 0;
    return -1 unless substr($f, $i, 2) eq reverse substr($s, $i, 2);

    return $i;
}
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-sauoq
"My two cents aren't worth a dime.";

The examples suggested that both strings were anagrams of each other. However, here's a fix:

sub comp {
    my ($f, $s) = @_;
    return -1 if length ($f) != length ($s);

    local $_ = $f ^ $s;
    return -1 unless tr/\x00/1/c == 2;

    my $r = index $_, "11";

   (substr ($f, $r, 2) eq reverse substr ($s, $r, 2)) ? $r : -1;
}
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Abigail

That does it. That's just a really cool solution. I didn't know xor worked on strings like that.

Or even shorter... Albeit about 3 times slower on long strings and 30% faster for short...

sub comp {
    local $_ = $_[0] ^ $_[1];
    return s/([^\x00])\1//g==1 && !tr/\x00/1/c;
}
[download]



T I M T O W T D I

Very cool. Can you explain why it works? What makes the XOR come out to be like that?

A massive flamewar beneath your chosen depth has not been shown here

Hey! Thats really elegant and instructive Abigail-II - but please forgive a stupid question...
Would it be possible for the product of $f ^ $s to contain a "1" and hence pollute your $_ string?


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- Johnson