my %dup; # duplicate charachters hash

print "<TABLE BORDER='1'>\n";
for (<DATA>) {
    chomp;
    next if /^\s*$/;
    my @elements = split", ",$_;        
    map{exists $dup{$_} ? $_= "&nbsp;" : $dup{$_}++ }@elements;
    print_row(@elements);
}
print "</TABLE>\n";

sub print_row {
    print"<TR>";
    print"<TD>$_</TD>" for @_;
    print"</TR>\n";
}


__DATA__
csc, tech, base
csc, comp, acm
csc, mous, base