51nod 1264线段相交（计算几何）

Posted 2022-02-08 SSL_LKJ

线段相交

题目传送门

输入样例

2
1 2 2 1 0 0 2 2
-1 1 1 1 0 0 1 -1

输出样例

Yes
NO

解题思路

用叉积和跨立实验判断

AC代码

#include<algorithm>
#include<cstdio>
using namespace std;
struct node

	double x,y;
a[5];
double cj(node x,node y,node z)

	return (x.x-z.x)*(y.y-z.y)-(x.y-z.y)*(y.x-z.x);

bool check(node x,node y,node z)

	if(z.x>=min(x.x,y.x)&&z.x<=max(x.x,y.x)&&z.y>=min(x.y,y.y)&&z.y<=max(x.y,y.y))return 1;
	return 0;

int main()

	int T;
	scanf("%d",&T);
	while(T--)
	
		int ok=0;
		for(int i=1;i<=4;i++)scanf("%lf%lf",&a[i].x,&a[i].y);
		if(cj(a[3],a[4],a[1])*cj(a[3],a[4],a[2])<0&&cj(a[1],a[2],a[3])*cj(a[1],a[2],a[4])<0)ok=1;
		if(!cj(a[1],a[2],a[3])&&check(a[1],a[2],a[3]))ok=1;
		if(!cj(a[1],a[2],a[4])&&check(a[1],a[2],a[4]))ok=1;
		if(!cj(a[3],a[4],a[1])&&check(a[3],a[4],a[1]))ok=1;
		if(!cj(a[3],a[4],a[2])&&check(a[3],a[4],a[2]))ok=1;
		if(ok)printf("Yes\\n");
		else printf("No\\n");
	
	return 0;
 

谢谢