国庆集训D1T3 小X的佛光

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/TengWan_Alunl/article/details/82917214

存双向边要开两倍空间！！！！！

#include<bits/stdc++.h>
#define rep(i,l,r) for(int i=(l);i<=(r);i++)
#define per(i,r,l) for(int i=(r);i>=(l);i--)
using namespace std;
const int N=4e5+1000;
int n,q,num;
int nxt[N],to[N],head[N],len;
int dep[N],fa[N][21];
void addedge(int u,int v){ nxt[++len]=head[u]; to[len]=v; head[u]=len; }
void dfs(int v,int dp,int father){
	dep[v]=dp; fa[v][0]=father;
	rep(i,1,20) fa[v][i]=fa[fa[v][i-1]][i-1];
	for(int i=head[v];i!=0;i=nxt[i]){//初始化为-1？？
		if(to[i]==father) continue;
		dfs(to[i],dp+1,v);
	}
}
int lca(int u,int v){
	if(dep[u]<dep[v]) return lca(v,u);
	per(i,20,0) if(dep[fa[u][i]]>=dep[v]) u=fa[u][i];
	if(u==v) return v;
	per(i,20,0) if(fa[u][i]!=fa[v][i]) u=fa[u][i],v=fa[v][i];
	return fa[u][0];
}
int main(){
	scanf("%d%d%d",&n,&q,&num);
	rep(i,1,n-1){
		int x,y; scanf("%d%d",&x,&y);
		addedge(x,y); addedge(y,x);
	}
	dfs(1,1,0);
	while(q--){
		int a,b,c,fab,fac,fbc,cent;
		scanf("%d%d%d",&a,&b,&c);
		fab=lca(a,b); fac=lca(a,c); fbc=lca(b,c);
		if(dep[fab]>dep[fac]) cent=fab; else cent=fac;
		if(dep[cent]<dep[fbc]) cent=fbc;
		printf("%d\n",dep[cent]+dep[b]-dep[lca(cent,b)]*2+1);
	}
	return 0;
}