极角排序+对称思想——poj2280

用对称的思想，每次极角排序前，把黑点按原点对称，就可以转换成为白点进行统计了

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
#define N 200005
#define db double
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;int c;
    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 getP() const{return sign(y)==1||(sign(y)==0&&sign(x)>=0);}
};
db cross(point k1,point k2){return k1.x*k2.y-k1.y*k2.x;}
db dot(point k1,point k2){return k1.x*k2.x+k1.y*k2.y;}

bool operator<(const point k1,const point k2){
    if(k1.getP()==k2.getP())return sign(cross(k1,k2))>0;
    return k1.getP()<k2.getP();
}

point p[N],pp[N];
int n,tot,ans;

void solve(int id){
    tot=0;
    for(int i=1;i<=n;i++)if(i!=id){
        pp[++tot]=p[i]-p[id];
        pp[tot].c=p[i].c;
        if(pp[tot].c==1){
            pp[tot].x*=-1;
            pp[tot].y*=-1;
        }
    }
    sort(pp+1,pp+1+tot);
    for(int i=1;i<=tot;i++)pp[tot+i]=pp[i];
    
    int num=1,pos=1;
    for(int i=1;i<=tot;i++){
        while(pos+1<i+tot && sign(cross(pp[i],pp[pos+1]))>=0)
            pos++,num++;
        ans=max(ans,num);
        num--;
    }
}

int main(){
    while(cin>>n && n){
        ans=0;
        for(int i=1;i<=n;i++)
            scanf("%lf%lf%d",&p[i].x,&p[i].y,&p[i].c);
        for(int i=1;i<=n;i++)
            solve(i);
        cout<<ans+1<<'\n';
    }
}