树分治

int tot,rt,mx,cnt,n,up;
int first[N],vis[N],sz[N],w[N];

void init(int n)
{
    tot=0;ans=0;
    for(int i=0;i<=n;i++)
    {
        vis[i]=0;
        first[i]=-1;
    }
}

void dfs1(int u,int fa)
{
    int maxv=1;
    sz[u]=1;
    for(int i=first[u];i!=-1;i=edge[i].next)
    {
        int v=edge[i].e;
        if(v==fa||vis[v]) continue;
        dfs1(v,u);
        sz[u]+=sz[v];
        maxv=max(maxv,sz[v]);
    }
    maxv=max(maxv,sz[0]-sz[u]);
    if(maxv<mx) mx=maxv,rt=u;
}

void dfs2(int u,int fa)
{
    sz[u]=1;
    for(int i=first[u];i!=-1;i=edge[i].next)
    {
        int v=edge[i].e;
        if(v==fa||vis[v]) continue;
        dfs2(v,u);
        sz[u]+=sz[v];
    }
}

LL solve(int u)
{

}

void dfs(int u,int num)
{
    sz[0]=num;
    mx=INF;
    dfs1(u,-1);//get_root
    vis[rt]=1;
    ans+=solve(rt);
    for(int i=first[rt];i!=-1;i=edge[i].next)
    {
        int v=edge[i].e;
        if(vis[v]) continue;
        ans-=solve(v);
    }
    for(int i=first[rt];i!=-1;i=edge[i].next)
    {
        int v=edge[i].e;
        if(vis[v]) continue;
        dfs(v,sz[v]);
    }
}