Diameter

vector<long> ed[MAX+7];
long di1[MAX+7];
long di2[MAX+7];

void Dfs( long u, long *di, vector<long> &li ){
    li.pb( u );
    long i;
    for( i=0;i<ed[u].size();i++ ){
        long v = ed[u][i];
        if( di[v] != -1 ) continue;
        di[v] = di[u] + 1; // can set cost instead of 1 for weigted tree
        Dfs( v, di, li );
    }
}

void Diam( long u, long &l, long &r ){
    vector<long> li;
    di1[u] = 0;
    Dfs( u, di1, li );

    long i,v1 = li[0];
    for( i=0;i<li.size();i++ ){
        if( di1[li[i]] > di1[v1] ) v1 = li[i];
    }

    li.clear();
    di2[v1] = 0;
    Dfs( v1, di2, li );

    long v2 = v1;
    for( i=0;i<li.size();i++ ){
        if( di2[li[i]] > di2[v2] ) v2 = li[i];
    }

    l = di2[v2];
    r = (l+1)/2;
}