Boundary

枚举两个点,而且还过(0,0)点,所以直接计算出所有的圆心,并用map保存

#include<bits/stdc++.h>
using namespace std;
const int MAXN=2005;
int n,ans;
double a[MAXN],b[MAXN],x,y;
typedef pair<double,double> p;
map<p,int> mx;
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%lf%lf",a+i,b+i);
    for(int i=1;i<=n;i++)
    {
        mx.clear();
        for(int j=i+1;j<=n;j++)
            if(a[i]*b[j]!=a[j]*b[i])
            {
                x=((b[j]-b[i])*b[i]*b[j]-a[i]*a[i]*b[j]+a[j]*a[j]*b[i])/(a[j]*b[i]-a[i]*b[j]);
                y=((a[j]-a[i])*a[i]*a[j]-b[i]*b[i]*a[j]+b[j]*b[j]*a[i])/(b[j]*a[i]-b[i]*a[j]);
                mx[p(x,y)]++; ans=max(mx[p(x,y)],ans);
            }
    }
    printf("%d\n",ans+1);
}