hdu 3622 二分+2-SAT判定

思路：如题

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<cmath>
#define Maxm 100010
#define eps 1e-4
using namespace std;
int vi[220],head[220],e,n,m,id[220],lab,num,dfn[220],low[220],Stack[220],top;
double Max;
struct Point{
    double x,y;
}p[210];
struct Edge{
    int u,v,next;
}edge[Maxm];
void init()
{
    memset(vi,0,sizeof(vi));
    memset(head,-1,sizeof(head));
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    lab=num=top=0;
    e=0;
}
void add(int u,int v)
{
    edge[e].u=u,edge[e].v=v,edge[e].next=head[u],head[u]=e++;
}
double Dis(Point a,Point b)
{
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
void Tarjan(int u)
{
    int i,j,v;
    dfn[u]=low[u]=++lab;
    Stack[top++]=u;
    vi[u]=1;
    for(i=head[u];i!=-1;i=edge[i].next)
    {
        v=edge[i].v;
        if(!dfn[v])
        {
            Tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        if(vi[v])
            low[u]=min(low[u],dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        ++num;
        do{
            i=Stack[--top];
            vi[i]=0;
            id[i]=num;
        }while(i!=u);
    }
}
int solve()
{
    int i,j;
    for(i=1;i<=2*n;i++)
        if(!dfn[i])
        Tarjan(i);
    for(i=1;i<=n;i++)
        if(id[i]==id[i+n])
        return 0;
    return 1;
}
void buildGraphic(double mid)
{
    init();
    int i,j;
    for(i=1;i<=n;i++)
    {
        for(j=i+1;j<=n;j++)
        {
            if(Dis(p[i],p[j])<mid)
                add(i,j+n),add(j,i+n);
            if(Dis(p[i+n],p[j+n])<mid)
                add(i+n,j),add(j+n,i);
        }
        for(j=1+n;j<=2*n;j++)
        {
            if(j==i+n) continue;
            if(Dis(p[i],p[j])<mid)
                add(i,j-n),add(j,i+n);
        }
    }
}
int main()
{
    int i,j;
    while(scanf("%d",&n)!=EOF)
    {
        init();
        for(i=1;i<=n;i++)
            scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i+n].x,&p[i+n].y);
        double l,r,mid;
        l=0,r=40000;
        while(l+eps<r)
        {
            mid=(l+r)/2;
            buildGraphic(mid*2);
            if(solve())
                l=mid;
            else
                r=mid;
        }
        printf("%.2lf
",l);
    }
    return 0;
}