ural 1215 Exactness of Projectile Hit 

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <cmath>
 4 #include <algorithm>
 5 #define maxn 20000
 6 using namespace std;
 7 const double eps=1e-8;
 8 
 9 inline double sqr(double x)
10 {
11     return x*x;
12 }
13 inline int dcmp(double x)
14 {
15     if(fabs(x)<eps) return 0;
16     else return x<0?-1:1;
17 }
18 struct node
19 {
20     double x,y;
21 }p[maxn];
22 
23 double dis(node a,node b)
24 {
25     return sqrt(sqr(a.x-b.x)+sqr(a.y-b.y));
26 }
27 
28 double cross(node a,node b,node c)
29 {
30     return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
31 }
32 
33 double dot(node a,node b)
34 {
35     return a.x*b.x+a.y*b.y;
36 }
37 bool in(node *p,int n,node a)
38 {
39     p[n]=p[0];p[n+1]=p[1];
40     for(int i=0; i<n; i++)
41     {
42         if(-cross(p[i],p[i+1],a)*cross(p[i+1],p[i+2],a)>eps)
43         {
44             return false;
45         }
46     }
47     return true;
48 }
49 
50 double disten(node pp,node a,node b)
51 {
52     if(a.x==b.x&&a.y==b.y) return dis(pp,a);
53     node st1;st1.x=b.x-a.x; st1.y=b.y-a.y;
54     node st2;st2.x=pp.x-a.x; st2.y=pp.y-a.y;
55     node st3;st3.x=pp.x-b.x; st3.y=pp.y-b.y;
56     if(dcmp(dot(st1,st2))<0) return dis(pp,a);
57     else if(dcmp(dot(st1,st3)>0)) return dis(pp,b);
58     else return fabs(cross(a,b,pp))/(dis(a,b));
59 }
60 
61 int main()
62 {
63     int n;
64     node c;
65     scanf("%lf%lf%d",&c.x,&c.y,&n);
66     double min1=1e10;
67     for(int i=0; i<n; i++)
68     {
69         scanf("%lf%lf",&p[i].x,&p[i].y);
70     }
71     if(in(p,n,c))
72     {
73         printf("%.3lf\n",0.0);
74     }
75     else
76     {
77         for(int i=0; i<n; i++)
78         {
79             min1=min(min1,disten(c,p[i],p[i+1]));
80         }
81         printf("%.3lf\n",2*min1);
82     }
83     return 0;
84 }
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posted @ 2014-03-22 23:21  null1019  阅读(123)  评论(0)    收藏  举报