mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
121 lines
3.2 KiB
C++
121 lines
3.2 KiB
C++
#pragma comment(linker, "/STACK:102400000,102400000")
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#include <stdio.h>
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#include <iostream>
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#include <algorithm>
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#include <sstream>
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#include <stdlib.h>
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#include <string.h>
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#include <limits.h>
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#include <string>
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#include <time.h>
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#include <math.h>
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#include <queue>
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#include <stack>
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#include <set>
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#include <map>
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using namespace std;
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#define INF 0x3f3f3f3f
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#define eps 1e-8
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#define pi acos(-1.0)
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typedef long long ll;
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int fun(){
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char ch;int flag=1,a=0;
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while(ch=getchar())if((ch>='0'&&ch<='9')||ch=='-')break;
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if(ch=='-')flag=-1;else a=ch-'0';
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while(ch=getchar()){
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if(ch>='0'&&ch<='9')a=10*a+ch-'0';
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else break;
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}
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return flag*a;
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}
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const int maxn=1001000;
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int head[maxn],tol;
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int subtree[maxn];
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int belong[maxn];
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int child[maxn][4];
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int que[maxn];
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int path[maxn];
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int fa[maxn];
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int dep[maxn];
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struct Edge{
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int next,to;
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}edge[2*maxn];
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void addedge(int u,int v){
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edge[tol].to=v;
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edge[tol].next=head[u];
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head[u]=tol++;
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}
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int main()
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{
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int n,m;
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while(~scanf("%d%d",&n,&m)){
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memset(head,-1,sizeof(head));tol=0;
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for(int i=1;i<n;i++){
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int u,v;
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u=fun();v=fun();
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addedge(u,v);
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addedge(v,u);
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}
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int front=0,rear=0;
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dep[1]=0;fa[1]=-1;
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que[rear++]=1;
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while(front!=rear){
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int u=que[front++];
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for(int i=head[u];i!=-1;i=edge[i].next){
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int v=edge[i].to;
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if(v==fa[u])continue;
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dep[v]=dep[u]+1;
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fa[v]=u;
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que[rear++]=v;
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}
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}
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for(int i=1;i<=n;i++)
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for(int j=0;j<4;j++)
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child[i][j]=INF;
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for(int i=rear-1;i>=0;i--){
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int u=que[i];
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subtree[u]=min(u,child[u][0]);
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int p=fa[u];
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if(p==-1)continue;
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child[p][3]=subtree[u];
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sort(child[p],child[p]+4);
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}
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front=0,rear=0;
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path[1]=INF;
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belong[1]=-1;
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for(int i=head[1];i!=-1;i=edge[i].next){
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int u=edge[i].to;
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path[u]=INF;
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belong[u]=subtree[u];
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que[rear++]=u;
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}
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while(front!=rear){
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int u=que[front++];
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for(int i=head[u];i!=-1;i=edge[i].next){
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int v=edge[i].to;
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if(v==fa[u])continue;
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path[v]=min(path[u],child[u][subtree[v]==child[u][0]]);
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belong[v]=belong[u];
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que[rear++]=v;
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}
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path[u]=min(path[u],child[u][0]);
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}
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int last=0;
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while(m--){
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int u,v;
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u=fun();v=fun();
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u^=last;v^=last;
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if(u>v)swap(u,v);
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if(u!=1&&belong[u]==belong[v])last=1;
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else{
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int i=0;
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while(child[1][i]==belong[u]||child[1][i]==belong[v])i++;
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last=u==1?path[v]:min(path[u],path[v]);
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last=min(last,child[1][i]);
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}
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printf("%d\n",last);
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}
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}
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return 0;
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}
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