PERL: Merge Sort Inverstion Times

MergeSortInversionTimes.pl

our $invTimes =0;
sub mergeSortInversions{
    my @x =@_;
    return @x if (@x < 2);
    my $mid = int (@x/2);
    my @a = mergeSortInversions(@x[0 .. $mid - 1]);
    my @b = mergeSortInversions(@x[$mid .. $#x]);

    for (my $i = 0; $i < @x; $i++) {
        if (!@a){
            $x[$i]=shift @b;
        }
        elsif (!@b){
            $x[$i]=shift @a;
        }
        elsif ($a[0]<=$b[0]){
            $x[$i]=shift @a;
        }
        else {
            $invTimes =$invTimes+@a;
            $x[$i]=shift @b;
            
        }
    }
    return(@x);
}
@array = mergeSortInversions(@array);
print "\n$invTimes\n";