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=210;
const int INF=0x3f3f3f3f;
const int MOD=5000,STA=100010;
const LL LNF=1LL<<60;
const double EPS=1e-8;
const double OO=1e15;
const int dx[4]={-1,0,1,0};
const int dy[4]={0,1,0,-1};
const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
//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][2];
int first[N],next[N*N*2],vis[N],S[N];
int n,mt,cnt;

struct Edge{
    int u,v;
}e[N*N*2];

double dist(int i,int j){
    return sqrt((double)((nod[i][0]-nod[j][0])*(nod[i][0]-nod[j][0])+
                (nod[i][1]-nod[j][1])*(nod[i][1]-nod[j][1])));
}

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^1])return 0;
    if(vis[u])return 1;
    int i;
    vis[u]=1;
    S[cnt++]=u;
    for(i=first[u];i!=-1;i=next[i]){
        if(!dfs(e[i].v))return 0;
    }
    return 1;
}

int Twosat()
{
    int i,j;
    for(i=0;i<n;i+=2){
        if(vis[i] || vis[i^1])continue;
        cnt=0;
        if(!dfs(i)){
            while(cnt)vis[S[--cnt]]=0;
            if(!dfs(i^1))return 0;
        }
    }
    return 1;
}

void init(double limt)
{
    int i,j;
    mt=0;mem(vis,0);
    mem(first,-1);
    for(i=0;i<n;i++){
        for(j=i+2;j<n;j++)if(d[i][j]<limt)adde(i,j^1),adde(j,i^1);
        i++;
        for(j=i+1;j<n;j++)if(d[i][j]<limt)adde(i,j^1),adde(j,i^1);
    }
}

double binary(double l,double r)
{
    double mid;
    while(fabs(l-r)>EPS){
        mid=(l+r)/2;
     //   printf("%.2lf %.2lf %.2lf
",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<<=1;
        for(i=0;i<n;i+=2){
            scanf("%d%d%d%d",&nod[i][0],&nod[i][1],&nod[i^1][0],&nod[i^1][1]);
        }
        hig=0;
        for(i=0;i<n;i++){
            for(j=i+1;j<n;j++){
                d[i][j]=d[j][i]=dist(i,j);
                hig=Max(hig,d[i][j]);
            }
        }

        printf("%.2lf
",binary(0,hig)/2);
    }
    return 0;
}