loj2182 「SDOI2015」寻宝游戏

#include <iostream>
#include <cstdio>
#include <set>
using namespace std;
typedef long long ll;
int n, m, ise[100005], fa[100005][19], dep[100005], uu, vv, ww, hea[100005], cnt;
int faq, nfd[100005];
ll dis[100005], ans;
struct Edge{
    int too, nxt, val;
}edge[200005];
struct Node{
    int idx, dfn;
    bool operator<(const Node &x)const{
        return dfn<x.dfn;
    }
};
set<Node> qwq;
void add_edge(int fro, int too, int val){
    edge[++cnt].nxt = hea[fro];
    edge[cnt].too = too;
    edge[cnt].val = val;
    hea[fro] = cnt;
}
void dfs(int x, int f, ll d){
    nfd[x] = ++faq;
    dis[x] = d;
    fa[x][0] = f;
    dep[x] = dep[f] + 1;
    for(int i=hea[x]; i; i=edge[i].nxt){
        int t=edge[i].too;
        if(t!=f)    dfs(t, x, d+edge[i].val);
    }
}
int queryPre(int x){
    set<Node>::iterator i=qwq.lower_bound((Node){x, nfd[x]});
    if(i==qwq.begin())  i = qwq.end();
    return (*(--i)).idx;
}
int queryNxt(int x){
    set<Node>::iterator i=qwq.lower_bound((Node){x, nfd[x]});
    if((++i)==qwq.end())    i = qwq.begin();
    return (*i).idx;
}
int lca(int x, int y){
    if(dep[x]<dep[y])   swap(x, y);
    for(int i=16; i>=0; i--)
        if(dep[fa[x][i]]>=dep[y])
            x = fa[x][i];
    if(x==y)    return x;
    for(int i=16; i>=0; i--)
        if(fa[x][i]!=fa[y][i]){
            x = fa[x][i];
            y = fa[y][i];
        }
    return fa[x][0];
}
ll qdis(int x, int y){
    return dis[x]+dis[y]-2*dis[lca(x, y)];
}
ll query(int x){
    int pre, nxt, fla;
    if(!ise[x]){
        fla = 1;
        qwq.insert((Node){x, nfd[x]});
        pre = queryPre(x);
        nxt = queryNxt(x);
    }
    else{
        fla = -1;
        pre = queryPre(x);
        nxt = queryNxt(x);
        qwq.erase((Node){x, nfd[x]});
    }
    ise[x] ^= 1;
    if(qwq.size()<=1)   ans = 0;
    else    ans += fla * (qdis(pre, x)+qdis(x, nxt)-qdis(pre, nxt));
    return ans;
}
int main(){
    cin>>n>>m;
    for(int i=1; i<n; i++){
        scanf("%d %d %d", &uu, &vv, &ww);
        add_edge(uu, vv, ww);
        add_edge(vv, uu, ww);
    }
    dfs(1, 0, 0);
    for(int i=1; i<=16; i++)
        for(int j=1; j<=n; j++)
            fa[j][i] = fa[fa[j][i-1]][i-1];
    while(m--){
        scanf("%d", &uu);
        printf("%lld\n", query(uu));
    }
    return 0;
}