Hdu 4458 Shoot The airplane (judging points within polygons)

Title Address: http://acm.hdu.edu.cn/showproblem.php?pid=4458

Idea: Aircraft as the reference system, the plane is relatively static, the bullet plus the horizontal direction of Speed-V. You only need to enumerate the time to determine if the time point (bullet) is within the polygon (plane). Note that G can be 0, evenly variable and uniform. In addition, the accuracy of the subject is high, the point of judgment in the line with the difference in coordinates, to avoid using dot.

#include <cstdio> #include <cstring> #include <iostream> #include <algorithm> #define Debuusing    Namespace Std;const Double eps = 1e-10;const int maxn=25;struct point{double x, y; Point (Double x = 0, double y = 0): x (x), Y (y) {}};typedef point vector;int n,v,b,g; Point P[MAXN]; Vector operator-(const point &a, const point &b) {return Vector (a.x-b.x, a.y-b.y);}    int dcmp (double x) {if (Fabs (x) < EPS) return 0; else return x < 0? -1:1;} Double Dot (const vector &a, const vector &b) {return a.x * b.x + a.y * B.Y;} Double Cross (const vector &a, const vector B) {return a.x * b.y-a.y * b.x;}  BOOL Onsegment (const-point &p, const-point &a1, const-point-&AMP;A2) {//return dcmp (cross (a1-p, a2-p)) = = 0    && dcmp (Dot (A1-p, a2-p)) < 0;    if (dcmp (Cross (a1-p,a2-p))) return 0; else if (dcmp (P.x-min (a1.x,a2.x)) >=0&&dcmp (P.x-max (a1.x,a2.x)) <=0&&dcmp (P.y-min (A1.Y,A2.Y) ) &GT;=0&AMP;&AMP;DCMP (P.y-max (A1.Y,A2.Y)) <=0) return 1; else return 0;}    int Ispointinpolygon (point P, point *poly, int n) {int wn = 0;        for (int i = 0; i < n; ++i) {if (Onsegment (p, Poly[i], poly[(i+1)%n])) return 0;        int k=dcmp (Cross (poly[(i+1)%n]-poly[i], p-poly[i]));        int d1=dcmp (POLY[I].Y-P.Y);        int d2=dcmp (poly[(i+1)%n].y-p.y);        if (k>0&&d1<=0&&d2>0) wn++;    if (k<0&&d2<=0&&d1>0) wn--;    } if (wn!=0) return 1; else return 0;}    int main () {#ifdef debug Freopen ("In.in", "R", stdin), #endif//debug while (scanf ("%d%d%d", &v,&b,&g) ==3)        {if (v==0&&b==0&&g==0) break;        scanf ("%d", &n);        Double maxy=0.0;            for (int i=0; i<n; i++) {scanf ("%lf%lf", &p[i].x,&p[i].y);        Maxy=max (MAXY,P[I].Y);        } int flag=0; Double time=dcmp (g)?        (2.0*b/g):(1.0*maxy/b);      cout<<time<<endl;  For (double i=0.0, i<=time; i+=0.001) {point tmp;            Tmp.x=-v*i,tmp.y=b*i-0.5*g*i*i;                if (Ispointinpolygon (tmp,p,n)) {printf ("%.2f\n", I);                flag=1;            Break    }} if (!flag) printf ("miss!\n"); } return 0;}

Hdu 4458 Shoot The airplane (judging points within polygons)