BZOJ 3910 并查集+线段树合并

思路：

1. 并查集+线段树合并

记得f[LCA]==LCA的时候 f[LCA]=fa[LCA]

2.LCT（并不会写啊...）

//By SiriusRen
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int N=;
int n,m,xx,yy,a,first[N],next[N*],v[N*],tot,deep[N],num[N],f[N],fa[N][];
long long ans;
int lca(int x,int y){
    if(deep[x]<deep[y])swap(x,y);
    for(int i=;~i;i--)if(deep[x]-(<<i)>=deep[y])x=fa[x][i];
    if(x==y)return x;
    for(int i=;~i;i--)if(fa[x][i]!=fa[y][i])x=fa[x][i],y=fa[y][i];
    return fa[x][];
}
void dfs(int x){for(int i=first[x];~i;i=next[i])if(v[i]!=fa[x][])deep[v[i]]=deep[x]+,fa[v[i]][]=x,dfs(v[i]);}
void add(int x,int y){v[tot]=y,next[tot]=first[x],first[x]=tot++;}
int dis(int x,int y){return deep[x]+deep[y]-*deep[lca(x,y)];}
int find(int x){return x==f[x]?x:f[x]=find(f[x]);}
int main(){
    memset(first,-,sizeof(first));
    scanf("%d%d%d",&n,&m,&a);
    for(int i=;i<n;i++){
        scanf("%d%d",&xx,&yy),add(xx,yy),add(yy,xx);
    }deep[]=,dfs();
    for(int j=;j<=;j++)
        for(int i=;i<=n;i++)
        fa[i][j]=fa[fa[i][j-]][j-];
    for(int i=;i<=m;i++)scanf("%d",&num[i]);
    for(int i=;i<=n;i++)f[i]=i;
    for(int i=;i<=m;i++){
        if(find(num[i])==num[i]){
            int LCA=lca(a,num[i]);
            ans+=dis(a,num[i]);
            for(int j=a;deep[j]>deep[LCA];j=find(fa[j][]))f[j]=LCA;
            for(int j=num[i];deep[j]>deep[LCA];j=find(fa[j][]))f[j]=LCA;
            if(f[LCA]==LCA)f[LCA]=fa[LCA][];
            a=num[i];
        }
    }
    printf("%lld\n",ans);
}