OJ-Problems-Source/HDOJ/4916_autoAC.cpp

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#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;
}