学步园

几何入门

先贴着http://blog.csdn.net/wangjian8006

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
#define eps 1e-8
#define maxn 110
struct Line
{
	double x1,y1,x2,y2;
	void input(double a,double b,double c,double d)
	{
		x1=a,y1=b,x2=c,y2=d;
	}
}L[maxn];
int n;

int sgn(double x)
{
	return x<-eps?-1:x>eps?1:0;
}
double dis(double x1,double y1,double x2,double y2)
{
	return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
double cross(double x1,double y1, double x2,double y2,double x,double y)
{
	return (x2-x1)*(y-y1)-(x-x1)*(y2-y1);
}
bool judge(double x1,double y1,double x2,double y2)
{
	if(dis(x1,y1,x2,y2)<eps) 
		return 0;
	for(int i=0;i<n;i++)
		if(cross(x1,y1,x2,y2,L[i].x1,L[i].y1)*cross(x1,y1,x2,y2,L[i].x2,L[i].y2)>eps) 
			return 0;
	return 1;
}
int main()
{
	int t;
	double a,b,c,d;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%d",&n);
		for(int i=0;i<n;i++)
		{
			scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
			L[i].input(a,b,c,d);
		}
		if(n==1)
		{
			printf("Yes!\n");
			continue;
		}
		int ans=0;
		for(int i=0;i<n&&!ans;i++)
			for(int j=i+1;j<n&&!ans;j++)
				if( judge(L[i].x1,L[i].y1,L[j].x1,L[j].y1) ||
					judge(L[i].x1,L[i].y1,L[j].x2,L[j].y2) ||
					judge(L[i].x2,L[i].y2,L[j].x1,L[j].y1) ||
					judge(L[i].x2,L[i].y2,L[j].x2,L[j].y2))
					ans=1;
		if(ans)
			printf("Yes!\n");
		else
			printf("No!\n");
	}
	return 0;
}