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;
}