poj 1106 Transmitters （叉乘的应用）

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <stdlib.h>
 4 #include <iostream>
 5 #include <algorithm>
 6 #include <math.h>
 7 #define eps 1e-6
 8 typedef struct point
 9 {
10     double x,y;
11 }point;
12 
13 bool  dy(double x,double y){ return x>y+eps; }
14 bool  xy(double x,double y){ return x<y-eps; }
15 bool dyd(double x,double y){ return x>y-eps; }
16 bool xyd(double x,double y){ return x<y+eps; }
17 bool  dd(double x,double y){ return fabs(x-y)<eps; }
18 
19 double crossProduct(point a,point b,point c)
20 {
21     return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
22 }
23 
24 double dist(point a,point b)
25 {
26     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
27 }
28 
29 point c[1005];
30 double st,en,ri;
31 point tmp;
32 int solve(int n)
33 {
34         int ans;
35         int maxx=0;
36         for(int i=0;i<n;i++)
37         {
38             ans=1;
39             for(int j=0;j<n;j++)
40             {
41                 if(i!=j&&dyd(crossProduct(tmp,c[i],c[j]),0.0))
42                 {
43                        ans++;
44                 }
45             }
46             if(ans>maxx)
47             {
48                 maxx=ans;
49                 //ans=0;
50             }
51         }
52         return maxx;
53 }
54 
55 int main()
56 {
57     int n;
58     double a,b;
59     while(scanf("%lf%lf%lf",&st,&en,&ri)!=EOF&&ri>=0)
60     {
61         point p;
62         tmp.x=st;
63         tmp.y=en;
64         scanf("%d",&n);
65         int cas=0;
66         for(int i=0;i<n;i++)
67         {
68             scanf("%lf%lf",&p.x,&p.y);
69             if(xyd(dist(tmp,p),ri))
70             {
71                 c[cas++]=p;
72             }
73         }
74         printf("%d\n",solve(cas));
75     }
76 }