poj1106

极角排序扫一圈。

今天没什么状态写个水题减轻负罪感(大雾)

#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
typedef double db;
const db eps = 1e-6;
const db pi = acos(-1);
int sign(db k){
    if (k>eps) return 1; else if (k<-eps) return -1; return 0;
}
int cmp(db k1,db k2){return sign(k1-k2);}
struct point{
    db x,y,ang;
    point operator + (const point &k1) const{return (point){k1.x+x,k1.y+y};}
    point operator - (const point &k1) const{return (point){x-k1.x,y-k1.y};}
    point operator * (db k1) const{return (point){x*k1,y*k1};}
    point operator / (db k1) const{return (point){x/k1,y/k1};}
    int operator == (const point &k1) const{return cmp(x,k1.x)==0&&cmp(y,k1.y)==0;}
    db abs(){ return sqrt(x*x+y*y);}
    db dis(point k1){return ((*this)-k1).abs();}
    db getw(){return atan2(y,x);}
};
struct circle{
    point o;db r;
    int inside(point k){return cmp(r,o.dis(k))>=0;}
}c;
vector<point> v;
bool cmp2(point a,point b){
    return a.ang<b.ang;
}
int n;point t;
int main(){
    while (scanf("%lf%lf%lf",&c.o.x,&c.o.y,&c.r)&&c.r>0){
    //scanf("%lf%lf%lf",&c.o.x,&c.o.y,&c.r);
        scanf("%d",&n);
        while (n--){
            scanf("%lf%lf",&t.x,&t.y);
            if(c.inside(t)){
                t.ang = (c.o-t).getw();
                v.push_back(t);
                v.push_back({t.x,t.y,t.ang+2*pi});
            }
        }
        sort(v.begin(),v.end(),cmp2);
        int m = v.size()/2;
        int ans = 0;
        for(int l=0,r=0;l<m;l++){
            while (r<2*m&&v[r].ang-v[l].ang<=pi)
                r++;
            ans=max(ans,r-l);
        }
        printf("%d
",ans);
        v.clear();
    }
}