$_=0;

Shouldn't this be
    local $_ = 0;
to avoid global variable side effects (see local)?

$_=0;
$x < $y && $_--;
$x > $y && $_++;
$_;
[download]

And how does this code differ in effect from
    $x <=> $y;
(see <=> in Equality Operators in perlop)?

(And a small point, but , (comma) is used as the delimiter in the OPed example data instead of : (colon), which you use in the s/:.+// extraction substitutions.)