在线LCA

const int MAXN = 10010;
const int MAXM = 10010;  

struct N
{
    int v,w,next;
}edge[MAXM*2];
int Top;
int head[MAXN];
int MAXSIZE;
int dep[MAXN];
int seq[MAXN*2];
int R[MAXN];  

struct ST
{
    int dep,point;
    bool operator < (const ST &A) const
    {
        return dep < A.dep;
    }
}st[MAXN*8];
  //若为无向图则w = 1。
void Link(int u,int v,int w)
{
    edge[Top].v = v;
    edge[Top].w = w;
    edge[Top].next = head[u];
    head[u] = Top++;
}  

void Init()
{
    memset(head,-1,sizeof(head));
    Top = 0;
    MAXSIZE = 0;
}  

void InitDep(int s,int pre = -1,int d = 0)
{
    R[s] = ++MAXSIZE;
    seq[MAXSIZE] = s;
    dep[s] = d;  

    for(int p =  head[s]; p != -1; p = edge[p].next)
    {
        if(edge[p].v != pre)
        {
            InitDep(edge[p].v,s,d+edge[p].w);
            seq[++MAXSIZE] = s;
        }
    }
}  

void InitST(int site,int l,int r)
{
    if(l == r)
    {
        st[site].dep = dep[seq[l]];
        st[site].point = seq[l];
        return ;
    }  

    int mid = (l+r)>>1;  

    InitST(site<<1,l,mid);
    InitST(site<<1|1,mid+1,r);  

    st[site] = st[site<<1].dep < st[site<<1|1].dep ? st[site<<1] : st[site<<1|1];
}  

ST QueryLCA(int site,int L,int R,int l,int r)
{
    if(L == l && R == r)
        return st[site];  

    int mid = (L+R)>>1;  

    if(r <= mid)
        return QueryLCA(site<<1,L,mid,l,r);
    else if(mid < l)
        return QueryLCA(site<<1|1,mid+1,R,l,r);  

    return min(QueryLCA(site<<1,L,mid,l,mid),QueryLCA(site<<1|1,mid+1,R,mid+1,r));  

}