HDU1756 几何+点在多边形内

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 1 /*
 2 几何+判定点是否在多边形内
 3 */
 4 #include<stdio.h>
 5 #include<string.h>
 6 #include<stdlib.h>
 7 #include<math.h>
 8 const int maxn = 105;
 9 const double eps = 1e-8;
10 const int inf = 99999999;
11 const int max_x = 1000;
12 const int max_y = 1000;
13 struct point{
14     double x,y;
15 };
16 point p1,p[ maxn ];
17 double xmult( point a,point b,point c ){
18     return ( b.x-a.x )*( c.y-a.y )-( b.y-a.y )*( c.x-a.x );
19 }
20 int zero( double x ){
21     if( x>eps )
22         return 1;
23     if( x<-eps )
24         return -1;
25     if( x<eps&&x>-eps )
26         return 0;
27 }
28 
29 int inPoly( int n ,point p1,point p[] ){
30     int count;
31     int i=0;
32     p[ n ]=p[ 0 ];
33     point p2;
34     while( i<n ){
35         p2.x = rand()+max_x;
36         p2.y = rand()+max_y;//随机选取一个远点
37         for( i=count=0;i<n;i++ ){
38             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 )
39             return true;//点在边上
40             else if( zero(xmult(p1,p2,p[i]))==0 )
41                 break;//p[i]在p1，p2上
42             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 )
43             count++;//枚举每条边，统计p1，p2和边的相交点的个数
44         }
45     }
46     return count & 1;
47 }
48 
49 int main() {
50     int n;
51     while (scanf("%d", &n) != EOF) {
52         for (int i=0; i<n; ++i) 
53             scanf ("%lf%lf", &p[i].x, &p[i].y);
54         int m;
55         scanf ("%d", &m);
56         while (m--) {
57             scanf ("%lf%lf", &p1.x, &p1.y);
58             if ( inPoly( n,p1,p )==true ) 
59                 printf ("Yes\n");
60             else
61                 printf ("No\n");
62         }
63     }
64     return 0;
65 }

 

posted @ 2013-03-19 14:11  xxx0624  阅读(342)  评论(0)  编辑  收藏  举报