121 lines
3.2 KiB
C++
121 lines
3.2 KiB
C++
#pragma comment(linker, "/STACK:102400000,102400000")
|
|
#include <stdio.h>
|
|
#include <iostream>
|
|
#include <algorithm>
|
|
#include <sstream>
|
|
#include <stdlib.h>
|
|
#include <string.h>
|
|
#include <limits.h>
|
|
#include <string>
|
|
#include <time.h>
|
|
#include <math.h>
|
|
#include <queue>
|
|
#include <stack>
|
|
#include <set>
|
|
#include <map>
|
|
using namespace std;
|
|
#define INF 0x3f3f3f3f
|
|
#define eps 1e-8
|
|
#define pi acos(-1.0)
|
|
typedef long long ll;
|
|
int fun(){
|
|
char ch;int flag=1,a=0;
|
|
while(ch=getchar())if((ch>='0'&&ch<='9')||ch=='-')break;
|
|
if(ch=='-')flag=-1;else a=ch-'0';
|
|
while(ch=getchar()){
|
|
if(ch>='0'&&ch<='9')a=10*a+ch-'0';
|
|
else break;
|
|
}
|
|
return flag*a;
|
|
}
|
|
const int maxn=1001000;
|
|
int head[maxn],tol;
|
|
int subtree[maxn];
|
|
int belong[maxn];
|
|
int child[maxn][4];
|
|
int que[maxn];
|
|
int path[maxn];
|
|
int fa[maxn];
|
|
int dep[maxn];
|
|
struct Edge{
|
|
int next,to;
|
|
}edge[2*maxn];
|
|
void addedge(int u,int v){
|
|
edge[tol].to=v;
|
|
edge[tol].next=head[u];
|
|
head[u]=tol++;
|
|
}
|
|
int main()
|
|
{
|
|
int n,m;
|
|
while(~scanf("%d%d",&n,&m)){
|
|
memset(head,-1,sizeof(head));tol=0;
|
|
for(int i=1;i<n;i++){
|
|
int u,v;
|
|
u=fun();v=fun();
|
|
addedge(u,v);
|
|
addedge(v,u);
|
|
}
|
|
int front=0,rear=0;
|
|
dep[1]=0;fa[1]=-1;
|
|
que[rear++]=1;
|
|
while(front!=rear){
|
|
int u=que[front++];
|
|
for(int i=head[u];i!=-1;i=edge[i].next){
|
|
int v=edge[i].to;
|
|
if(v==fa[u])continue;
|
|
dep[v]=dep[u]+1;
|
|
fa[v]=u;
|
|
que[rear++]=v;
|
|
}
|
|
}
|
|
for(int i=1;i<=n;i++)
|
|
for(int j=0;j<4;j++)
|
|
child[i][j]=INF;
|
|
for(int i=rear-1;i>=0;i--){
|
|
int u=que[i];
|
|
subtree[u]=min(u,child[u][0]);
|
|
int p=fa[u];
|
|
if(p==-1)continue;
|
|
child[p][3]=subtree[u];
|
|
sort(child[p],child[p]+4);
|
|
}
|
|
front=0,rear=0;
|
|
path[1]=INF;
|
|
belong[1]=-1;
|
|
for(int i=head[1];i!=-1;i=edge[i].next){
|
|
int u=edge[i].to;
|
|
path[u]=INF;
|
|
belong[u]=subtree[u];
|
|
que[rear++]=u;
|
|
}
|
|
while(front!=rear){
|
|
int u=que[front++];
|
|
for(int i=head[u];i!=-1;i=edge[i].next){
|
|
int v=edge[i].to;
|
|
if(v==fa[u])continue;
|
|
path[v]=min(path[u],child[u][subtree[v]==child[u][0]]);
|
|
belong[v]=belong[u];
|
|
que[rear++]=v;
|
|
}
|
|
path[u]=min(path[u],child[u][0]);
|
|
}
|
|
int last=0;
|
|
while(m--){
|
|
int u,v;
|
|
u=fun();v=fun();
|
|
u^=last;v^=last;
|
|
if(u>v)swap(u,v);
|
|
if(u!=1&&belong[u]==belong[v])last=1;
|
|
else{
|
|
int i=0;
|
|
while(child[1][i]==belong[u]||child[1][i]==belong[v])i++;
|
|
last=u==1?path[v]:min(path[u],path[v]);
|
|
last=min(last,child[1][i]);
|
|
}
|
|
printf("%d\n",last);
|
|
}
|
|
}
|
|
return 0;
|
|
}
|