hdu1077计算几何

根据atan函数求出β的值，再用中点坐标与β的值求出圆形的坐标。

#include <iostream>
#include <cmath>
const double eps = 1e-6;
const int MAXN = 305;
struct node
{
    double x, y;
};
struct node ps[MAXN];
int N;

double dis(node a, node b) {
    return sqrt(pow(a.x - b.x, 2) + pow(a.y - b.y, 2));
}

node cent0(node a, node b) {
    double midx = (a.x + b.x) / 2;
    double midy = (a.y + b.y) / 2;
    double l = sqrt(1 - pow(dis(a, b) / 2, 2));
    double dx = a.x - b.x;
    double dy = a.y - b.y;
    node po;
    if (dy < 1e-6) {
        po.x = midx;
        po.y = midy + l;
    }
    else {
        double angle = atan(dx / dy);
        po.x = midx + l * cos(angle);
        po.y = midy - l * sin(angle);
    }
    return po;
}

node cent1(node a, node b) {
    double midx = (a.x + b.x) / 2;
    double midy = (a.y + b.y) / 2;
    double l = sqrt(1 - pow(dis(a, b) / 2, 2));
    double dx = a.x - b.x;
    double dy = a.y - b.y;
    node po;
    if (fabs(dy) < 1e-6) {
        po.x = midx;
        po.y = midy - l;
    }
    else {
        double angle = atan(dx / dy);
        po.x = midx - l * cos(angle);
        po.y = midy + l * sin(angle);
    }
    return po;
}


int main()
{
    int T, i, j, k, max0,max1;
    scanf_s("%d", &T);
    while (T--)
    {
        scanf_s("%d", &N);
        for (i = 0; i < N; i++)
            scanf_s("%lf%lf", &ps[i].x, &ps[i].y);
        int ans = 1;
        for (i = 0; i < N; i++)//枚举O(n^2)
        {
            for (j = i + 1; j < N; j++)
            {
                if (dis(ps[i], ps[j]) >= 2) continue;

                node c0 = cent0(ps[i], ps[j]);
                node c1 = cent1(ps[i], ps[j]);

                for (k = 0, max0 = 0, max1 = 0; k < N; k++)
                {
                    //if (N - k + max <= ans) break;
                    double temp0 = dis(ps[k],c0);
                    double temp1 = dis(ps[k], c1);
                    if (temp0 <= 1.000001) {
                        max0++;
                    }
                    if (temp1 <= 1.000001) {
                        max1++;
                    }
                }

                if (max0 > ans) {
                    ans = max0;
                }
                if (max1> ans) {
                    ans = max1;
                }
            }
        }
        printf("%d\n", ans);
    }
    return 0;
}