hdu1077模擬

解析幾何，用參數方程解

#include <iostream>
#include <math.h>
using namespace std;
typedef struct P
{
    double x;
    double y;
};
double dist(P p1,P p2)
{
    return sqrt((p1.y-p2.y)*(p1.y-p2.y)+(p1.x-p2.x)*(p1.x-p2.x));
}
double gett(P p1,P p2)
{
   return  sqrt(1-(dist(p1,p2)/2)*(dist(p1,p2)/2));
}


double getsita(P p1,P p2)
{
    double sita;
    sita=atan(-(p1.x-p2.x)/(p1.y-p2.y));
    return sita;
}


int main()
{
    int n,i,j,ans,num,k;
    double x1,y1,x2,y2,xm,ym,sita,t;
    P temp,p[400],mid;
    int T;
    cin>>T;
    while (T--)
    {
    cin>>n;
    ans=1;
    for (i=1;i<=n;i++) cin>>p[i].x>>p[i].y;

    for (i=1;i<=n;i++)
        for (j=i+1;j<=n;j++)
    if (dist(p[i],p[j])<1.0001*2)
    {
       xm=(p[i].x+p[j].x)/2;
       ym=(p[i].y+p[j].y)/2;
       mid.x=xm;
       mid.y=ym;
       t=gett(p[i],p[j]);
       sita=getsita(p[i],p[j]);
      // cout<<xm<<" "<<ym<<" "<<t<<" "<<sita<<endl;
       x1=xm+cos(sita)*t;
       y1=ym+sin(sita)*t;
       x2=xm-cos(sita)*t;
       y2=ym-sin(sita)*t;
       temp.x=x1;
       temp.y=y1;
       num=0;
     // cout<<temp.x<<" "<<temp.y<<endl;
       for (k=1;k<=n;k++)
        {

            if (dist(temp,p[k])<1.0001) num++;
        }
        if (num>ans) ans=num;


        temp.x=x2;
       temp.y=y2;
       num=0;
     //  cout<<temp.x<<" "<<temp.y<<endl;
       for (k=1;k<=n;k++)
        {

            if (dist(temp,p[k])<1.0001) num++;
        }
        if (num>ans) ans=num;
    }
    cout<<ans<<endl;
    }
    return 0;
}