HDU 3622 Bomb Game(2

#include<cstdio>
#include<cstring>
#include<vector>
#include<cmath>
using namespace std;
const int maxn=100+10;
int n;
struct TwoSAT
{
    int n;
    vector<int> G[maxn*2];
    int S[maxn*2],c;
    bool mark[maxn*2];

    bool dfs(int x)
    {
        if(mark[x^1]) return false;
        if(mark[x]) return true;
        mark[x]=true;
        S[c++]=x;

        for(int i=0;i<G[x].size();i++)
            if(!dfs(G[x][i])) return false;
        return true;
    }

    void init(int n)
    {
        this->n=n;
        for(int i=0;i<2*n;i++) G[i].clear();
        memset(mark,0,sizeof(mark));
    }

    void add_clause(int x,int xval,int y,int yval)
    {
        x = x*2+xval;
        y = y*2+yval;
        G[x].push_back(y);
    }

    bool solve()
    {
        for(int i=0;i<2*n;i+=2)
        if(!mark[i] && !mark[i+1])
        {
            c=0;
            if(!dfs(i))
            {
                while(c>0) mark[S[--c]]=false;
                if(!dfs(i+1)) return false;
            }
        }
        return true;
    }
}TS;
struct Point
{
    double x,y;
};
struct Node
{
    Point p[2];
}s[maxn];
double dist(int i,int vi,int j,int vj)
{
    double x1,y1,x2,y2;
    x1 = s[i].p[vi].x;
    y1 = s[i].p[vi].y;
    x2 = s[j].p[vj].x;
    y2 = s[j].p[vj].y;
    return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
bool ok(double mid)
{
    TS.init(n);
    for(int i=0;i<n;i++)
    for(int j=i+1;j<n;j++)
    {
        if(dist(i,0,j,0) < mid*2) //冲突
        {
            TS.add_clause(i,0,j,1);
            TS.add_clause(j,0,i,1);
        }
        if(dist(i,1,j,0) < mid*2) //冲突
        {
            TS.add_clause(i,1,j,1);
            TS.add_clause(j,0,i,0);
        }
        if(dist(i,0,j,1) < mid*2) //冲突
        {
            TS.add_clause(i,0,j,0);
            TS.add_clause(j,1,i,1);
        }
        if(dist(i,1,j,1) < mid*2) //冲突
        {
            TS.add_clause(i,1,j,0);
            TS.add_clause(j,1,i,0);
        }
    }
    return TS.solve();
}
int main()
{
    while(scanf("%d",&n)==1)
    {
        for(int i=0;i<n;i++)
        {
            scanf("%lf%lf%lf%lf",&s[i].p[0].x,&s[i].p[0].y,&s[i].p[1].x,&s[i].p[1].y);
        }
        double L=0.0, R=20000.1;
        while(R-L > (1e-4) )
        {
            double mid = (R+L)/2;
            if(ok(mid)) L=mid;
            else R=mid;
        }
        printf("%.2lf\n",L);
    }
    return 0;
}