【定径圆覆盖最多点模板】

#define eps 1e-9#define pi acos(-1.0)#define N 222struct point{    double x,y;}p[N];struct alpha{    double v;    bool flag;    bool friend operator <(const alpha &a,const alpha &b){//排序专用偏序关系       return a.v < b.v;    }}alp[N * 2];double dis(point a, point b){    return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));}int n;void solve(double R){//传入定径圆的半径    int ans = 0;    double theta,phi,dist;    for(int i = 0;i < n;i++){       int k = 0;       for(int j = 0;j < n;j++){           if(i == j) continue;           dist = dis(p[i],p[j]);           if(dist > 2.0 * R)              continue;           theta = atan2(p[j].y - p[i].y, p[j].x - p[i].x);           if(theta < 0)              theta += 2 * pi;           phi = acos(dist / (2.0 * R));           alp[k].v = theta - phi + 2 * pi;           alp[k].flag = true;           alp[k + 1].v = theta + phi + 2 * pi;           alp[k + 1].flag = false;           k += 2;       }       sort(alp,alp + k);       int sum = 0;       for(int j = 0;j < k;j++){           if(alp[j].flag)              sum ++;           else              sum --;           if(sum > ans)              ans = sum;       }    }    printf("%d\n",ans + 1);}