hdu 4793 Collision（几何）

题目链接：hdu 4793 Collision

代码

#include <cstdio>#include <cstring>#include <cmath>#include <vector>#include <algorithm>using namespace std;const double pi = 4 * atan(1);const double eps = 1e-6;inline int dcmp(double x) { if (fabs(x) < eps) return 0; else return x < 0 ? -1 : 1; }inline double torad(double deg) { return deg / 180 * pi; }struct Point {    double x, y;    Point (double x = 0, double y = 0): x(x), y(y) {}    void read() { scanf("%lf%lf", &x, &y); }    Point operator + (const Point& p) { return Point(x+p.x, y+p.y); }    Point operator - (const Point& p) { return Point(x-p.x, y-p.y); }};typedef Point Vector;double getDot (Vector a, Vector b) { return a.x * b.x + a.y * b.y; }//double getCross (Vector a, Vector b) { return a.x * b.y - a.y * b.x; }double getLength (Vector a) { return sqrt(getDot(a, a)); }struct Circle {    Point o;    double r;    Circle() {}    Circle(Point o, double r): o(o), r(r) {}};int getLineCircleIntersection(Point p, Vector v, Circle O, double& t1, double& t2) {    double a = v.x, b = p.x - O.o.x, c = v.y, d = p.y - O.o.y;    double e = a*a+c*c, f = 2*(a*b+c*d), g = b*b+d*d-O.r*O.r;    double delta = f*f - 4*e*g;    if (dcmp(delta) < 0) return 0;    if (dcmp(delta) == 0) {        t1 = t2 = -f / (2*e);        return 1;    }    t1 = (-f - sqrt(delta)) / (2*e);    t2 = (-f + sqrt(delta)) / (2*e);    return 2;}double Rm, R, r, X, Y, VX, VY;int main () {    while (scanf("%lf%lf%lf%lf%lf%lf%lf", &Rm, &R, &r, &X, &Y, &VX, &VY) == 7) {        double t1, t2, ans = 0;        Point P = Point(X, Y);        Vector V = Vector(VX, VY);        int tmp = getLineCircleIntersection(P, V, Circle(Point(0, 0), Rm+r), t1, t2);        if (tmp && dcmp(t1) >= 0) {            double k = t1;            getLineCircleIntersection(P, V, Circle(Point(0, 0), R+r), t1, t2);            ans = (2 * k - t1 - max(t1, 0.0));        } else if (getLineCircleIntersection(P, V, Circle(Point(0, 0), R+r), t1, t2)) {            t1 = max(t1, 0.0); t2 = max(t2, 0.0);            ans = (t2-t1);        }        printf("%.3lf\n", ans);    }    return 0;}