POJ 1208 极角序

//Result:wizmann	1228	Accepted	268K	79MS	C++	2943B

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <iostream>

#include <algorithm>

#include <cmath>

#include <bitset>

#include <deque>



using namespace std;



#define print(x) cout<<x<<endl

#define input(x) cin>>x

#define SIZE 1024



const double inf=1e100;

const double eps=1e-8;



inline int zero(double x)

{

    if(x<-eps) return -1;

    else if(fabs(x)<eps) return 0;

    else return 1;

}



struct point

{

	double x,y;

	point(){}

	point(double i_x,double i_y)

	{

		x=i_x;y=i_y;

	}

	friend bool operator == (const point& pa,const point& pb)

	{

		return (!zero(pa.x-pb.x)) && (!zero(pa.y-pb.y));

	}

};



struct line

{

	double a,b,c;

	line(){}

	line(double i_a,double i_b,double i_c)

	{

		a=i_a;b=i_b;c=i_c;

	}

};



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);

}



double pointDis(point p1,point p2)

{

	return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));

}



line makeline(point p1,point p2)

{

	line res;

	int sig=1;

	res.a=p2.y-p1.y;

	if(zero(res.a)<0)

	{

		sig=-1;

		res.a=sig*res.a;

	}

	res.b=sig*(p1.x-p2.x);

	res.c=sig*(p1.y*p2.x-p2.y*p1.x);

	return res;

}



struct cmp

{

    point p;

    cmp(const point &i_p)

    {

        p=i_p;

    }

    bool operator()(const point &a,const point &b)

	{

		if(zero(xmult(a,b,p))==0)	return pointDis(a,p)<pointDis(b,p);

		return zero(xmult(a,b,p))>0;

	}

};





int n;

point polygen[SIZE];



int findtop()

{

	int res=0;

	for(int i=0;i<n;i++)

	{

		if(polygen[i].y<polygen[res].y) res=i;

		else if(polygen[i].y==polygen[res].y && polygen[i].x<polygen[res].x) res=i;

	}

	return res;

}



bool slove()

{

	bitset<SIZE> visit;

	int edge=0;

	visit.reset();

	for(int i=0;i<n;i++) if(!visit[i])

	{

		bitset<SIZE> inque;

		int now=i;

		line l=makeline(polygen[now],polygen[(now+1)%n]);

		deque<int> dq;

		dq.push_back(now);

		int ptr=now+1;

		while(1)

		{

			if(!inque[ptr] && zero(l.a*polygen[ptr].x+l.b*polygen[ptr].y+l.c)==0)

			{

				inque[ptr]=1;

				dq.push_back(ptr);

				ptr=(ptr+1)%n;

			}

			else break;

		}

		ptr=(now-1+n)%n;

		while(1)

		{

			if(!inque[ptr] && zero(l.a*polygen[ptr].x+l.b*polygen[ptr].y+l.c)==0)

			{

				inque[ptr]=1;

				dq.push_front(ptr);

				ptr=(ptr-1+n)%n;

			}

			else break;

		}

		//print(dq.size());

		if(dq.size()<3) return false;

		else

		{

			edge++;

			dq.pop_front();

			dq.pop_back();

			for(int j=0;j<(int)dq.size();j++) visit[dq[j]]=1;

		}

	}

	return edge>=3;

}

		

		



int main()

{

	int T;

	double a,b;

	input(T);

	while(T--)

	{

		input(n);

		for(int i=0;i<n;i++)

		{

			scanf("%lf%lf",&a,&b);

			polygen[i]=point(a,b);

		}

		int ptr=findtop();

		swap(polygen[0],polygen[ptr]);

		for(int i=1;i<n;i++)

		{

			sort(polygen+i,polygen+n,cmp(polygen[i-1]));

		}

		if(slove()) print("YES");

		else print("NO");

	}

	return 0;

}