#include <cstdio>
#include <cstring>
#define MAX 500005
int d[MAX],fa[MAX],size[MAX],top[MAX],son[MAX];
int N,M,S,tot=0;
int head[MAX];
struct edge{
int v,next;
}G[MAX<<1];
inline void add(int u,int v){
G[++tot].v=v;G[tot].next=head[u];head[u]=tot;
}
inline void dfs1(int u,int father){
d[u]=d[father]+1;
fa[u]=father;
size[u]=1;
int max = 0;
for(register int i=head[u];i;i=G[i].next){
int v = G[i].v;
if(v==father)continue;
dfs1(v,u);
size[u]+=size[v];
if(size[v]>max)son[u]=v,max=size[v];
}
}
inline void dfs2(int u,int high,int father){
top[u]=high;
if(son[u]==0)return;
dfs2(son[u],high,u);
for(register int i=head[u];i;i=G[i].next){
int v = G[i].v;
if(v==son[u]||v==father)continue;
dfs2(v,v,u);
}
}
inline void swap(int* u,int* v){
int t = *u;*u = *v;*v = t;
}
inline int LCA(int u,int v){
while(top[u]!=top[v]){
if(d[top[u]]<d[top[v]])swap(&u,&v);
u = fa[top[u]];
}
return d[u]>d[v]?v:u;
}
int main(){
std::memset(head,0,sizeof(head));
std::memset(son,0,sizeof(son));
scanf("%d%d%d",&N,&M,&S);
int u,v;
for(register int i=1;i<N;++i){
scanf("%d%d",&u,&v);
add(u,v);add(v,u);
}
d[0]=0;
dfs1(S,0);
dfs2(S,0,0);
for(register int i=1;i<=M;++i){
scanf("%d%d",&u,&v);
printf("%d\n",LCA(u,v));
}
return 0;
}
原文地址:https://www.cnblogs.com/Neworld2002/p/8641002.html
时间: 2024-10-05 04:02:24