UVa 438 - The Circumference of the Circle

链接

传送门

题意

给出三角形三个顶点坐标，求三角形外接圆半径。

思路

套用外心模版。

代码

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;

struct Point {
  double x, y;
  Point() {}
  Point(double x, double y): x(x), y(y) {}
} A, B, C;

double Length(const Point& a) {
  return sqrt(a.x * a.x + a.y * a.y);
}

int main() {
  while (~scanf("%lf%lf%lf%lf%lf%lf", &A.x, &A.y, &B.x, &B.y, &C.x, &C.y)) {
    Point p;
    double a1 = B.x - A.x, b1 = B.y - A.y, c1 = (a1 * a1 + b1 * b1) / 2;
    double a2 = C.x - A.x, b2 = C.y - A.y, c2 = (a2 * a2 + b2 * b2) / 2;
    double d = a1 * b2 - a2 * b1;
    p.x = (c1 * b2 - c2 * b1) / d;
    p.y = (a1 * c2 - a2 * c1) / d;
    double r = Length(p);
    printf("%.2f\n", M_PI * r * 2);
  }
  return 0;
}