HDU-3622 Bomb Game 2sat

　　题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3622

　　题意：一个平面上有很多的炸弹，每个炸弹的爆炸范围是一样的，求最大的爆炸范围使得炸弹之间不相互影响。

　　二分爆炸范围，然后建立2sat模型，看是否存在解。

 //STATUS:C++_AC_171MS_972KB
 #include <functional>
 #include <algorithm>
 #include <iostream>
 //#include <ext/rope>
 #include <fstream>
 #include <sstream>
 #include <iomanip>
 #include <numeric>
 #include <cstring>
 #include <cassert>
 #include <cstdio>
 #include <string>
 #include <vector>
 #include <bitset>
 #include <queue>
 #include <stack>
 #include <cmath>
 #include <ctime>
 #include <list>
 #include <set>
 #include <map>
 using namespace std;
 //using namespace __gnu_cxx;
 //define
 #define pii pair<int,int>
 #define mem(a,b) memset(a,b,sizeof(a))
 #define lson l,mid,rt<<1
 #define rson mid+1,r,rt<<1|1
 #define PI acos(-1.0)
 //typedef
 typedef long long LL;
 typedef unsigned long long ULL;
 //const
 const int N=;
 const int INF=0x3f3f3f3f;
 const int MOD=,STA=;
 const LL LNF=1LL<<;
 const double EPS=1e-;
 const double OO=1e15;
 const int dx[]={-,,,};
 const int dy[]={,,,-};
 const int day[]={,,,,,,,,,,,,};
 //Daily Use ...
 inline int sign(double x){return (x>EPS)-(x<-EPS);}
 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
 template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
 template<class T> inline T Min(T a,T b){return a<b?a:b;}
 template<class T> inline T Max(T a,T b){return a>b?a:b;}
 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
 //End

 double d[N][N];
 int nod[N][];
 int first[N],next[N*N*],vis[N],S[N];
 int n,mt,cnt;

 struct Edge{
     int u,v;
 }e[N*N*];

 double dist(int i,int j){
     return sqrt((double)((nod[i][]-nod[j][])*(nod[i][]-nod[j][])+
                 (nod[i][]-nod[j][])*(nod[i][]-nod[j][])));
 }

 void adde(int a,int b)
 {
     e[mt].u=a,e[mt].v=b;
     next[mt]=first[a];first[a]=mt++;
 }

 int dfs(int u)
 {
     if(vis[u^])return ;
     if(vis[u])return ;
     int i;
     vis[u]=;
     S[cnt++]=u;
     for(i=first[u];i!=-;i=next[i]){
         if(!dfs(e[i].v))return ;
     }
     return ;
 }

 int Twosat()
 {
     int i,j;
     for(i=;i<n;i+=){
         if(vis[i] || vis[i^])continue;
         cnt=;
         if(!dfs(i)){
             while(cnt)vis[S[--cnt]]=;
             if(!dfs(i^))return ;
         }
     }
     return ;
 }

 void init(double limt)
 {
     int i,j;
     mt=;mem(vis,);
     mem(first,-);
     for(i=;i<n;i++){
         for(j=i+;j<n;j++)if(d[i][j]<limt)adde(i,j^),adde(j,i^);
         i++;
         for(j=i+;j<n;j++)if(d[i][j]<limt)adde(i,j^),adde(j,i^);
     }
 }

 double binary(double l,double r)
 {
     double mid;
     while(fabs(l-r)>EPS){
         mid=(l+r)/;
      //   printf("%.2lf %.2lf %.2lf\n",l,r,mid);
         init(mid);
         if(Twosat())l=mid;
         else r=mid;
     }
     return mid;
 }

 int main()
 {
  //   freopen("in.txt","r",stdin);
     int i,j;
     double hig;
     while(~scanf("%d",&n))
     {
         n<<=;
         for(i=;i<n;i+=){
             scanf("%d%d%d%d",&nod[i][],&nod[i][],&nod[i^][],&nod[i^][]);
         }
         hig=;
         for(i=;i<n;i++){
             for(j=i+;j<n;j++){
                 d[i][j]=d[j][i]=dist(i,j);
                 hig=Max(hig,d[i][j]);
             }
         }

         printf("%.2lf\n",binary(,hig)/);
     }
     return ;
 }