題意：給定原點及n個點，找到一個圓使得儘可能多的點在圓上
題解：三點可以確定一個圓，原點固定，遍歷兩個點去確定圓心，並用map儲存圓心，當再次得到一個相同的圓心時，map++（圓心相同，且有共點必定為同一個圓）

#include<iostream>
#include<stdio.h>
#include<math.h>
#include<map>
using namespace std;
const int maxn = 2e3+10;
const double eps=1e-5;
struct Point{
    double x,y;
}a[maxn];
map
 
<pair<double,double>,int> mp; 
int main(){
    int n;
    cin>>n;
    for(int i=1;i<=n;i++){
        scanf("%lf %lf",&a[i].x,&a[i].y);
    }
    int ans = 0;
    for(int i=1;i<=n;i++){
        mp.clear();
        for(int j=i+1;j<=n;j++){
            double x1 = a[i].x,x2 = a[j].x,y1 = a[i].y,y2 = a[j].y;
            
 
double x3=0,y3=0;
            double a = x1-x2;
            double b = y1-y2;
            double c = x1-x3;
            double d = y1-y3;
            double e = ((x1*x1-x2*x2)+(y1*y1-y2*y2))/2.0;
            double f = ((x1*x1-x3*x3)+(y1*y1-y3*y3))/2.0;
            double det = b*c-a*d;
            if(fabs(det)<eps){
                
 
continue;
            }
            double x = -(d*e-b*f)/det;
            double y = -(a*f-c*e)/det;
            ans = max(ans,++mp[{x,y}]);
            
        }
    }
    cout<<ans+1<<endl;
    return 0;
}