POJ3178 计算几何+DP

 //一些点一些圆，过圆不能连线，相邻点不能连线，问最多连几条线
 //计算几何模板+区间dp
 //关键是判断圆和线段是否相交
 #include <cstdio>
 #include <cmath>
 #include <algorithm>
 #define N 500
 #define ll long long
 #define sqr(x) ((x)*(x))
 using namespace std;
 bool ok[N][N];
 ll n,m,r,f[N][N];
 struct poi
 {
     ll x,y;
     poi(ll X,ll Y)
     {
         x=X;y=Y;
     }
     poi()
     {
     }
 } p[N],q[N];
 ll cro(poi a,poi b)
 {
     return (a.x*b.y-a.y*b.x);
 }
 ll dot(poi a,poi b)
 {
     return a.x*b.x+a.y*b.y;
 }
 poi tr(poi a,poi b)
 {
     return poi(a.x-b.x,a.y-b.y);
 }
 double dis(poi a,poi b)
 {
     return sqrt((double)(sqr(a.x-b.x)+sqr(a.y-b.y)));
 }
 bool cmp(poi a,poi b)
 {
     return (a.x<b.x)||(a.x==b.x && a.y<b.y);
 }
 bool cmp2(poi a,poi b)
 {
     return cro(tr(a,p[]),tr(b,p[]))>;
 }
 bool check(poi a,poi b)
 {
     double C=dis(a,b);
     for(int i=;i<=m;i++)
     {
         double A=dis(q[i],a);
         double B=dis(q[i],b);
         double COSA=(B*B+C*C-A*A)/(*B*C);
         double COSB=(A*A+C*C-B*B)/(*A*C);
         if(COSA<1e-||COSB<1e-){
             if(A<1.0*r+1e-||B<1.0*r+1e-)return ;
             else continue;
         }
         double SINA=sqrt(-COSA*COSA);
         double H=B*SINA;
         if(H<1.0*r+1e-)return ;
     }
     return ;
 }
 int main()
 {
     scanf("%d%d%d",&n,&m,&r);
     for(int i=;i<=n;i++)
         scanf("%d%d",&p[i].x,&p[i].y);
     sort(p+,p++n,cmp);
     sort(p+,p++n,cmp2);
     for(int i=;i<=m;i++)
         scanf("%d%d",&q[i].x,&q[i].y);
     for(int i=;i<=n;i++)
         for(int j=i+;j<=n;j++)
         if(i!= || j!=n)
             ok[i][j]=check(p[i],p[j]);
     for(int len=;len<=n;len++)
         for(int start=;start<=n;start++){
             ll end=start+len;
             for(int k=start+;k<min(end,n);k++)
                 f[start][end]=max(f[start][end],f[start][k]+f[k][end]);
             f[start][end]+=ok[start][end];
         }
     printf("%d\n",f[][n]);
 }