NOIp2010 关押罪犯

二分+2-SAT

先预处理出所有的v，然后离散化一下，在那个的基础上二分，对于每次二分出的值约束边权超过所二分出的边权的两点。

 //OJ 1322
 //by Cydiater
 //2015.8.26
 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <queue>
 #include <map>
 #include <ctime>
 #include <string>
 #include <algorithm>
 #include <iomanip>
 #include <cstdlib>
 #include <cmath>
 using namespace std;
 #define ll long long
 #define up(i,j,n)       for(int i=j;i<=n;i++)
 #define down(i,j,n)     for(int i=j;i>=n;i--)
 ;
 const int oo=0x3f3f3f3f;
 inline int read(){
       ,f=;
       ;ch=getchar();}
       +ch-';ch=getchar();}
       return x*f;
 }
 map<int,int>m;
 ,cnt=,num[MAXN],leftt,rightt,len=,group[MAXN],group_num,dfn[MAXN],low[MAXN],stack[MAXN],node[MAXN][],part=,dfs_clock=;
 bool vis[MAXN];
 struct edge{
       int y,next,x;
 }e[MAXN];
 struct Prison{
       int x,y,v;
 }a[MAXN];
 namespace solution{
       inline void insert(int x,int y){e[++len].next=LINK[x];LINK[x]=len;e[len].y=y;e[len].x=x;}
       void init(){
             N=read();M=read();
             tmp[++top]=;
             up(i,,M){
                   a[i].x=read();a[i].y=read();a[i].v=read();
                   tmp[++top]=a[i].v;
             }
             sort(tmp+,tmp+top+);
             up(i,,top)if(!m[tmp[i]]){
                   m[tmp[i]]=++cnt;
                   num[cnt]=tmp[i];
             }
             up(i,,N)up(j,,)node[i][j]=++part;
       }
       void tarjan(int node){
             dfn[node]=low[node]=++dfs_clock;
             vis[node]=;stack[++top]=node;
             for(int i=LINK[node];i;i=e[i].next)
                   if(!dfn[e[i].y]){
                         tarjan(e[i].y);
                         low[node]=min(low[node],low[e[i].y]);
                   }else if(vis[e[i].y]) low[node]=min(low[node],dfn[e[i].y]);
             if(low[node]==dfn[node]){
                   int tmp;group_num++;
                   do{
                         tmp=stack[top--];
                         vis[tmp]=;
                         group[tmp]=group_num;
                   }while(tmp!=node);
             }
       }
       bool check(int xx){
             len=;top=;dfs_clock=;group_num=;
             memset(LINK,,sizeof(LINK));
             memset(dfn,,sizeof(dfn));
             memset(vis,,sizeof(vis));
             up(i,,M)if(a[i].v>xx){
                   int x=a[i].x,y=a[i].y;
                   //cout<<x<<' '<<y<<endl;
                   insert(node[x][],node[y][]);
                   insert(node[y][],node[x][]);
                   insert(node[x][],node[y][]);
                   insert(node[y][],node[x][]);
             }
             up(i,,N<<)if(!dfn[i])tarjan(i);
             up(i,,N)]]==group[node[i][]]);
             ;
       }
       void slove(){
             leftt=;rightt=cnt;
             <rightt){
                   ;
                   if(check(num[mid]))     rightt=mid;
                   else                    leftt=mid;
             }
       }
       void output(){
             if(check(num[leftt])){
                   cout<<num[leftt]<<endl;
             }else
                   cout<<num[rightt]<<endl;
       }
 }
 int main(){
       //freopen("input.in","r",stdin);
       using namespace solution;
       init();
       slove();
       output();
       ;
 }