URAL 1966

幾何模板

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<cmath>
using namespace std;

const double eps = 1e-8;

int dcmp(double d) {
    return d < -eps ? -1 : d > eps;
}

struct Point {
    double x, y;
    Point() {}
    Point(double x, double y)
    : x(x), y(y) {}

    Point operator + (const Point& a) const {
        return Point(x + a.x, y + a.y);
    }
    Point operator - (const Point& a) const {
        return Point(x - a.x, y - a.y);
    }
    Point operator * (double k) const {
        return Point(x * k, y * k);
    }
    Point operator / (double k) const {
        return Point(x / k, y / k);
    }
    double cross(const Point& a) const {
        return (x * a.y - y * a.x);
    }
    double dot(const Point& a) const {
        return x * a.x + y * a.y;
    }
    void read() {
        scanf("%lf%lf", &x, &y);
    }
    bool operator < (const Point& a) const {
        return x < a.x || (x == a.x && y < a.y);
    }
    bool operator == (const Point& a) const {
        return dcmp(x - a.x) == 0 && dcmp(y - a.y) == 0;
    }
    double length() {
        return sqrt(x * x + y * y);
    }
};
struct Line {
    Point a, b;

    Line() {}
    Line(const Point& a, const Point& b)
    :a(a), b(b) {}

    bool onSegment(Point p) {// 判斷點是否在線段上 
        return dcmp((p - a).cross(b - a)) == 0 && dcmp((a - p).dot(b - p)) <= 0;
    }
    int segCrossSeg(const Line &u) {// 判斷線段是否相交 
        int d1 = dcmp((b - u.a).cross(a - u.a));
        int d2 = dcmp((b - u.b).cross(a - u.b));
        int d3 = dcmp((u.b - a).cross(u.a - a));
        int d4 = dcmp((u.b - b).cross(u.a - b));
        if ((d1 ^ d2) == -2 && (d3 ^ d4) == -2) return 2;
        return ((d1 == 0 && dcmp((b - u.a).dot(a - u.a)) <= 0)
            || (d2 == 0 && dcmp((b - u.b).dot(a - u.b)) <= 0)
            || (d3 == 0 && dcmp((u.b - a).dot(u.a - a)) <= 0)
            || (d4 == 0 && dcmp((u.b - b).dot(u.a - b)) <= 0));
    }
};
//************************模板********************************************// 
Point p[250];
int fa[250];
int eu[250],ev[250];
int n,m;
int getFather(int x){
	if(fa[x]==-1)
		return x;
	return fa[x]=getFather(fa[x]);
}
int main() {

	while(cin>>n>>m)
	{
		memset(fa,-1,sizeof(fa));
		for(int i=1;i<=n;i++)
			p[i].read();
		for(int i=1;i<=m;i++)
		{
			cin>>eu[i]>>ev[i];
			int fu=getFather(eu[i]);
			int fv=getFather(ev[i]);
			if(fu!=fv)
				fa[fu]=fv;
		}
		for(int i=1;i<=m;i++)
		{
			Line l(p[eu[i]],p[ev[i]]);
			for(int j=1;j<=n;j++)
			{
				if(l.onSegment(p[j])==0)continue;
				int fu=getFather(j);
				int fv=getFather(eu[i]);
				if(fu!=fv)
					fa[fu]=fv;
			}
		}
		for(int i=1;i<=m;i++)
			for(int j=i+1;j<=m;j++)
			{
				Line l1(p[eu[i]],p[ev[i]]);
				Line l2(p[eu[j]],p[ev[j]]);
				if(l1.segCrossSeg(l2)==0)continue;
				int fu=getFather(eu[j]);
				int fv=getFather(eu[i]);
				if(fu!=fv)
					fa[fu]=fv;
			}
		int cnt=0;
		for(int i=1;i<=n;i++)
			if(fa[i]==-1)
				cnt++;
		 if (cnt == 1) puts("YES");
    	else puts("NO");
	}
    return 0;
}