BZOJ 1787 紧急集合

LCA。注意细节。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxv 500500
#define maxe 1005000
using namespace std;
int n,m,x,y,z,g[maxv],nume=0,anc[maxv][23],dis[maxv];
struct edge
{
    int v,nxt;
}e[maxe];
void addedge(int u,int v)
{
    e[++nume].v=v;
    e[nume].nxt=g[u];
    g[u]=nume;
}
void dfs(int x)
{
    for (int ee=1;ee<=20;ee++)
        anc[x][ee]=anc[anc[x][ee-1]][ee-1];
    for (int i=g[x];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if (v!=anc[x][0])
        {
            anc[v][0]=x;dis[v]=dis[x]+1;
            dfs(v);
        }
    }
}
int lca(int x,int y)
{
    if (dis[x]<dis[y]) swap(x,y);
    for (int e=20;e>=0;e--)
    {
        if ((dis[anc[x][e]]>=dis[y]) && (anc[x][e]!=0))
            x=anc[x][e];
    }
    if (x==y) return x;
    for (int ee=20;ee>=0;ee--)
    {
        if (anc[x][ee]!=anc[y][ee])
        {
            x=anc[x][ee];
            y=anc[y][ee];
        }
    }
    return anc[x][0];
}
int get_dis(int x,int y)
{
    int k=lca(x,y);
    return dis[x]+dis[y]-2*dis[k];
}
int main()
{
    scanf("%d%d",&n,&m);
    for (int i=1;i<=n-1;i++)
    {
        scanf("%d%d",&x,&y);
        addedge(x,y);
        addedge(y,x);
    }
    dfs(1);
    for (int i=1;i<=m;i++)
    {
        scanf("%d%d%d",&x,&y,&z);
        int t1,t2,t3;
        t1=lca(x,y);t2=lca(x,z);t3=lca(y,z);
        int ans1,ans2=0;
        if (t1==t2) ans1=t3;
        else if (t1==t3) ans1=t2;
        else ans1=t1;
        ans2=get_dis(x,ans1)+get_dis(y,ans1)+get_dis(z,ans1);
        printf("%d %d
",ans1,ans2);
    }
    return 0;
}