[Template] diameter tree

void ZJ ( int BH) 
{ 
    Sign [BH] = . 1 ;
     for ( int I = head [BH]; I; I = A [I] .next) 
    { 
        int Y = A [I] .to;
         IF ! ( Sign [Y]) 
        { 
            ZJ (Y); 
            zhijing = max (zhijing, SUM [BH] + SUM [Y] + A [I] .val); 
            SUM [BH] = max (SUM [BH], SUM [Y] + A [I] .val); // do not order these two trans! ! ! 
        } 
    } 
}