P3320 [SDOI2015]寻宝游戏（数剖+定理

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int N=3e5+10;
struct node{
    int nxt,to;ll val;
}d[N];int head[N],tot=0;
void add(int a,int b,ll c){
    d[++tot]={head[a],b,c};head[a]=tot;
}
int fa[N][18],depth[N],dfn[N],rdfn[N],tt=0;ll val[N];
int n,q;
void dfs(int x,int f){
    depth[x]=depth[f]+1;
    fa[x][0]=f;
    for(int i=1;i<18;i++){fa[x][i]=fa[fa[x][i-1]][i-1];}
    for(int i=head[x];i;i=d[i].nxt){
        int v=d[i].to;if(v==f) continue;
        dfs(v,x);
    }
}
int query(int a,int b){
    if(depth[a]<depth[b]) swap(a,b);
    for(int i=17;i>=0;i--){
        if(depth[fa[a][i]]>=depth[b]) a=fa[a][i];
    }
    if(a==b) return a;
    for(int i=17;i>=0;i--){
        if(fa[a][i]!=fa[b][i]){
            a=fa[a][i];b=fa[b][i];
        }
    }
    return fa[a][0];
}
void dfs2(int x,int f){
    dfn[x]=++tt;rdfn[tt]=x;
    for(int i=head[x];i;i=d[i].nxt){
        int to=d[i].to;if(to==f) continue;
        val[to]+=d[i].val+val[x];
        dfs2(to,x);
    }
}
ll getdis(int a,int b){
    int lcapos=query(a,b);
    return -val[lcapos]*2+val[a]+val[b];
}
set<int> s;
int vis[N];
int main(){
    scanf("%d%d",&n,&q);
    for(int i=1;i<=n;i++) vis[i]=-1;
    for(int i=1;i<=n-1;i++){
        int x,y,z;scanf("%d%d%d",&x,&y,&z);
        add(x,y,z);add(y,x,z);
    }
    dfs(1,0);dfs2(1,0);
    ll ans=0;
//    for(int i=1;i<=n;i++){
//        cout<<dfn[i]<<endl;
//    }
    while(q--){
        int y;scanf("%d",&y);
        vis[y]=-vis[y];
//        cout<<vis[y]<<endl;
//        cout<<dfn[y]<<endl;
        if(vis[y]==1){
            int x=dfn[y];
            s.insert(x);
            auto pos=s.find(x);
            int l,r;
            if(pos==s.begin()){
                l=*prev(s.end());
            }else{
                pos--;
                l=*(pos);
            }
            pos=s.find(x);pos++;
            if(pos==s.end()){
                r=*(s.begin());
            }else{
                r=*pos;
            }
            l=rdfn[l],r=rdfn[r];
            x=rdfn[x];
//            cout<<l<<" "<<r<<endl;
            ans+=getdis(x,l)+getdis(r,x)-getdis(l,r);
        }else{
            int x=dfn[y];
            auto pos=s.find(x);
            int l,r;
            if(pos==s.begin()){
                l=*prev(s.end());
            }else{
                pos--;
                l=*(pos);
            }
            pos=s.find(x);pos++;
            if(pos==s.end()){
                r=*(s.begin());
            }else{
                r=*pos;
            }
            s.erase(x);
            l=rdfn[l],r=rdfn[r];
            x=rdfn[x];
//            cout<<l<<" "<<r<<endl;
            ans-=getdis(x,l)+getdis(r,x)-getdis(l,r);
        }
        cout<<ans<<endl;
    }
}

标签：P3320,数剖,val,int,ll,pos,fa,SDOI2015,rdfn
来源： https://blog.csdn.net/weixin_45714303/article/details/121164004