HDU1756 几何+点在多边形内

详见代码

/*
几何+判定点是否在多边形内
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
const int maxn = 105;
const double eps = 1e-8;
const int inf = 99999999;
const int max_x = 1000;
const int max_y = 1000;
struct point{
    double x,y;
};
point p1,p[ maxn ];
double xmult( point a,point b,point c ){
    return ( b.x-a.x )*( c.y-a.y )-( b.y-a.y )*( c.x-a.x );
}
int zero( double x ){
    if( x>eps )
        return 1;
    if( x<-eps )
        return -1;
    if( x<eps&&x>-eps )
        return 0;
}

int inPoly( int n ,point p1,point p[] ){
    int count;
    int i=0;
    p[ n ]=p[ 0 ];
    point p2;
    while( i<n ){
        p2.x = rand()+max_x;
        p2.y = rand()+max_y;//随机选取一个远点
        for( i=count=0;i<n;i++ ){
            if( zero( xmult( p1,p[i],p[i+1] ) )==0 && (p[i].x-p1.x)*(p[i+1].x-p1.x)<eps && (p[i].y-p1.y)*(p[i+1].y-p1.y)<eps )
            return true;//点在边上
            else if( zero(xmult(p1,p2,p[i]))==0 )
                break;//p[i]在p1，p2上
            else if( xmult( p[i],p[i+1],p1 )*xmult( p[i],p2,p[i+1])>eps&&xmult( p1,p2,p[i] )*xmult( p1,p[i+1],p2 )>eps )
            count++;//枚举每条边，统计p1，p2和边的相交点的个数
        }
    }
    return count & 1;
}

int main() {
    int n;
    while (scanf("%d", &n) != EOF) {
        for (int i=0; i<n; ++i) 
            scanf ("%lf%lf", &p[i].x, &p[i].y);
        int m;
        scanf ("%d", &m);
        while (m--) {
            scanf ("%lf%lf", &p1.x, &p1.y);
            if ( inPoly( n,p1,p )==true ) 
                printf ("Yes\n");
            else
                printf ("No\n");
        }
    }
    return 0;
}