画圆

https://www.acwing.com/problem/content/4502/



思路：

首先要理解题目的意思，尤其是第一句话。然后分类讨论两种情况何时圆的面积最大。

代码

#include
#include
#include
#include
using namespace std;
const double eps = 1e-8;
int cmp(double x, double y)
{
if (fabs(x - y) if (x return 1;
}
int main()
{
double r, x1, y1, x2, y2;
scanf("%lf%lf%lf%lf%lf", &r, &x1, &y1, &x2, &y2);
double dx = x1 - x2;
double dy = y1 - y2;
double d = sqrt(dx * dx + dy * dy);
if (cmp(d, r) >= 0) printf("%lf %lf %lf\n", x1, y1, r);
else
{
if (!cmp(x1, x2) && !cmp(y1, y2))
printf("%lf %lf %lf\n", x1 + r / 2, y1, r / 2);
else
{
double r2 = (r + d) / 2;
double x = x2 + (x1 - x2) / d * r2;
double y = y2 + (y1 - y2) / d * r2;
printf("%lf %lf %lf\n", x, y, r2);
}
}
return 0;
}