My first try at golf:

sub b {  
    $M = scalar keys %t;
    $m = $M *= $M;
    foreach  ( keys %t ) {
        $r = c( $_ );
        ($m,$n) = ($r, $_) if ($r < $m );
    }
    $n;
}

sub c {
    @s=@_;
    %b  = ( $s[0] => $b=$sum=0 );
    while ( @s > 0 ) {
        $b ++;
        @s = grep {  ! exists( $b{$_}  ) } 
             map { @{$t{$_}} } @s;
        @b{ @s } = ($b) x scalar(@s);
        $sum += $b * scalar(@s); 
        return $M if $sum >  $m         
    }
    $sum;    
}
[download]

works for graphs too, I think.

Update: I can write that down in 196:

sub b{$M=$m=@_*@_;for(keys %t){$r=c($_);($m,$n)=($r,$_)if($r<$m)}$n}su
+b c{%b=($_[0]=>$b=$sum=1);while(@_){$b++;@_=grep{!$b{$_}}map{@{$t{$_}
+}}@_;@b{@_}=($b)x@_;$sum+=$b*@_;return$M if$sum>$m}$sum}
[download]

slower but shorter: down to 177:

sub b{$M=$m=@_*@_;for(keys %t){$r=c($_);($m,$n)=($r,$_)if($r<$m)}$n}su
+b c{%b=($_[0]=>$b=$sum=1);while(@_){$b++;@_=grep{!$b{$_}}map{@{$t{$_}
+}}@_;@b{@_}=($b)x@_;$sum+=$b*@_}$sum}
[download]

I never new how hard obfuscation is! </code>

--
Brigitte    'I never met a chocolate I didnt like'    Jellinek
http://www.horus.com/~bjelli/         http://perlwelt.horus.at