【Ahoi2008】【lca】【bzoj1787】Meet 紧急集合

题目链接：http://www.lydsy.com/JudgeOnline/problem.php?id=1787

题解：

求出三个点两两之间的lca会发现有两个是一样的，然后我们选那个不一样的就好了。

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;
struct use{
  int st,en;
}b[5000001];
int cnt,u,v,point[500001],next[5000001],deep[500001],fa[500001][20],n,m,x,y,z,aa,bb,cc,vis[1000001];
void add(int x,int y)
{
	++cnt;next[cnt]=point[x];point[x]=cnt;
	b[cnt].st=x;b[cnt].en=y;
}
void dfs(int x)
{
	 vis[x]=1;
	for (int i=1;i<=15;i++)
     {
	  if ((1<<i)>deep[x]) break;
	  fa[x][i]=fa[fa[x][i-1]][i-1];
     }
	for (int i=point[x];i;i=next[i])
	{
		if (vis[b[i].en]) continue;
		  	deep[b[i].en]=deep[x]+1;
		  	fa[b[i].en][0]=x;
		  	dfs(b[i].en);
	}
}
int lca(int x,int y)
{
	int t;
	if (deep[x]<deep[y]) swap(x,y);
	t=deep[x]-deep[y];
	for (int i=0;i<=15;i++)
	  if ((1<<i)&t) x=fa[x][i];
	for (int i=15;i>=0;i--)
	  	 if (fa[x][i]!=fa[y][i])
	  	 {
	  	 	 x=fa[x][i];
	  	 	 y=fa[y][i];
	  	 }
	if (x==y) return x;
	else return fa[x][0];
}
int main()
{
	scanf("%d%d",&n,&m);
	for (int i=1;i<=n-1;i++)
	  {
	  	 scanf("%d%d",&u,&v);
	  	 add(u,v);add(v,u);
	  }
	for (int i=0;i<=15;i++) fa[1][i]=1;
	dfs(1);
    for (int i=1;i<=m;i++)
    {
       int tt,zu;
	   scanf("%d%d%d",&x,&y,&z);
       aa=lca(x,y);bb=lca(x,z);cc=lca(y,z);
       if (aa==bb) zu=cc;if (aa==cc) zu=bb;if (bb==cc) zu=aa;
       aa=lca(zu,x);bb=lca(zu,y);cc=lca(zu,z);
       tt=-(deep[aa]-deep[zu])-(deep[aa]-deep[x])-(deep[bb]-deep[zu])-(deep[bb]-deep[y])-(deep[cc]-deep[zu])-(deep[cc]-deep[z]);
       printf("%d %d\n",zu,tt);
    }
}