POJ 1106 Transmitters(计算几何)

题目链接

切计算几何，感觉计算几何的算法还不熟。此题，枚举线段和圆点的直线，平分一个圆

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
using namespace std;
#define eps 1e-8
struct point
{
    double x,y;
}p[201];
double dis(point p1,point p2)
{
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}
double xmult(point p1,point p2,point p0)
{
    return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
}
int main()
{
    point r;
    double d;
    int n,m,i,j,ans,temp;
    while(scanf("%lf%lf%lf",&r.x,&r.y,&d)!=EOF)
    {
        if(d < 0) break;
        scanf("%d",&n);
        m = 0;
        for(i = 0;i < n;i ++)
        {
            scanf("%lf%lf",&p[i].x,&p[i].y);
        }
        for(i = 0;i < n;i ++)
        {
            if(dis(p[i],r) > d)
            continue;
            p[m++] = p[i];
        }
        ans = 0;
        for(i = 0;i < m;i ++)
        {
            temp = 0;
            for(j = 0;j < m;j ++)
            {
                if(xmult(p[i],p[j],r) >= 0)
                temp ++;
            }
            ans = max(ans,temp);
        }
        printf("%d
",ans);
    }
    return 0;
}

。