@anew = shrink(\@a, \@b);

sub shrink
{
    my %seen;
    my @ret;

    warn ("input arrays not the same length")
        unless scalar @{$_[0]} == scalar @{$_[1]};

    for my $i ( 0..scalar @{$_[1]} )
    {
        push @ret, $_[0]->[$i]
            unless $seen{$_[1]->[$i]};

        $seen{$_[1]->[$i]} = 1;
    }

    return @ret;
}
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