UVA 11796Dog Distance[平面几何]

#include "bits/stdc++.h"
using namespace std;
const int maxn = 100;
const double eps=1e-8;
struct Point {
    double x, y;
    Point(double x = 0, double y = 0):x(x), y(y) {}
};
typedef Point Vector;
Point operator + (Point A, Point B) {
    return Point(A.x+B.x, A.y+B.y);
}
Point operator - (Point A, Point B) {
    return Point(A.x-B.x, A.y-B.y);
}
Point operator * (Point A, double p) {
    return Point(A.x*p, A.y*p);
}
Point operator / (Point A, double p) {
    return Point(A.x/p, A.y/p);
}
bool operator < (const Point& a, const Point& b) {
    return a.x<b.x || (a.x==b.x && a.y<b.y);
}
int dcmp(double x) {
    if (fabs(x)<eps) return 0;return x<0?-1:1;
}
bool operator == (const Point& a, const Point &b) {
    return dcmp(a.x-b.x) == 0 && dcmp(a.y-b.y)==0;
}
double Dot(Point A, Point B) {
    return A.x*B.x+A.y*B.y;
}
//带方向的叉积，cross(x,y)=-cross(y,x)
double Cross(Point A, Point B) {
    return A.x*B.y - A.y*B.x;
}
double Length(Point A) {return sqrt(Dot(A,A));}
//向量之间的夹角
double DistanceToSegment(Point P, Point A, Point B) {
    if (A == B) return Length(P-A);
    Vector v1=B-A,v2=P-A,v3=P-B;
    if (dcmp(Dot(v1,v2)<0)) return Length(v2);
    else if(dcmp(Dot(v1,v3))>0) return Length(v3);
    else return fabs(Cross(v1,v2))/Length(v1);
}
void GetPoint(Point& P) {
    scanf("%lf%lf", &P.x, &P.y);
}
Point a[maxn], b[maxn];
int main(int argc, char const *argv[])
{
    int T;
    int Kcase = 0;
    scanf("%d", &T);
    while (T--) {
        int A, B;
        double lena = 0;
        double lenb = 0;
        scanf("%d%d", &A, &B);
        double minn = 0x3f3f3f3f, maxx = 0;
        for (int i = 0; i < A; i++) GetPoint(a[i]);
        for (int i = 0; i < B; i++) GetPoint(b[i]);
        int cnta = 0, cntb = 0;
        for (int i = 1; i < A; i++) lena += Length(a[i]-a[i-1]);
        for (int i = 1; i < B; i++) lenb += Length(b[i]-b[i-1]);
        double Va = lena, Vb = lenb;
        Point Pa = a[0], Pb = b[0];
        while (cnta < A-1 && cntb < B-1) {
            double La = Length(a[cnta+1]-Pa);
            double Lb = Length(b[cntb+1]-Pb);
            double time = min(La/Va, Lb/Vb);
            Vector Da = (a[cnta+1]-Pa)/La*time*Va;
            Vector Db = (b[cntb+1]-Pb)/Lb*time*Vb; 
            minn = min(minn, DistanceToSegment(Pa, Pb, Pb+Db-Da));
            maxx = max(maxx, Length(Pa-Pb));
            maxx = max(maxx, Length(Pa-Pb-Db+Da));
            Pa = Pa + Da; Pb = Pb + Db;
            if (Pa == a[cnta+1]) cnta++;
            if (Pb == b[cntb+1]) cntb++;
        }
        printf("Case %d: %.0lf\n", ++Kcase, maxx-minn);
    }
    return 0;
}