poj 1106(半圆围绕圆心旋转能够覆盖平面内最多的点)

#include<stdio.h>
#include<iostream>
#include<string.h>
#include <stdlib.h>
#include<math.h>
#include<algorithm>
using namespace std;
const int N = 160;
const double eps = 1e-8;
struct Point{
    double x,y;
}p[N],circle;
struct Line{
    Point a,b;
}line;
double r;
int n;
int cross(Point a,Point b,Point c){
    double ans = (a.x-c.x)*(b.y-c.y)-(b.x-c.x)*(a.y-c.y);
    if(fabs(ans)<eps) return 0;
    if(ans<0) return 1;
    return -1;
}
int main(){
    while(true){
        scanf("%lf%lf%lf",&circle.x,&circle.y,&r);
        if(r<=0) break;
        scanf("%d",&n);
        int k = 0;
        for(int i=0;i<n;i++){
            double x,y;
            scanf("%lf%lf",&x,&y);
            if((x-circle.x)*(x-circle.x)+(y-circle.y)*(y-circle.y)>r*r) continue;
            p[k].x = x;
            p[k++].y = y;
         }
         int temp1 ,temp2,mx = 0; ///mx要赋值为0，因为有可能一个点都没有,习惯赋值成-1被坑了一把
         for(int i=0;i<k;i++){
            line.a = p[i];
            line.b = circle;
            temp1=temp2 =0;
            for(int j=0;j<k;j++){
                if(cross(p[j],line.a,line.b)==0) {
                    temp1++;
                    temp2++;
                }else if(cross(p[j],line.a,line.b)==1){
                    temp1++;
                }else temp2++;
            }
            int ans = max(temp1,temp2);
            mx = max(ans,mx);
         }
         printf("%d\n",mx);
    }
    return 0;
}