枚举两点（端点），循环遍历与直线相交的线段。
1 #include <iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 #include<stdlib.h> 6 #include<vector> 7 #include<cmath> 8 #include<queue> 9 #include<set> 10 using namespace std; 11 #define N 105 12 #define LL long long 13 #define INF 0xfffffff 14 const double eps = 1e-10; 15 const double pi = acos(-1.0); 16 const double inf = ~0u>>2; 17 struct point 18 { 19 double x,y; 20 point(double x=0,double y = 0):x(x),y(y){} 21 }p[N<<1]; 22 struct line 23 { 24 point a,b; 25 }; 26 typedef point pointt ; 27 pointt operator -(point a,point b) 28 { 29 return point(a.x-b.x,a.y-b.y); 30 } 31 int dcmp(double x) 32 { 33 if(fabs(x)<eps) return 0; 34 return x<0?-1:1; 35 } 36 double cross(point a,point b) 37 { 38 return a.x*b.y-a.y*b.x; 39 } 40 double xmult(point a,point b,point c) 41 { 42 return cross(a-c,b-c); 43 } 44 int dotline(point p,line l) 45 { 46 return (!dcmp(xmult(p,l.a,l.b)))&&(l.a.x-p.x)*(l.b.x-p.x)<eps 47 &&(l.a.y-p.y)*(l.b.y-p.y)<eps; 48 } 49 double dis(point a) 50 { 51 return sqrt(a.x*a.x+a.y*a.y); 52 } 53 int Intersection( point a,point b,point c,point d ) 54 { 55 int d1,d2; 56 d1 = dcmp(xmult( a,c,b )); 57 d2 = dcmp(xmult( a,d,b )); 58 if( d1*d2==-1 ) return 1;//规范相交 59 if( d1==0||d2==0 ) return 2;//非规范相交 60 return 0;//不相交 61 } 62 int main() 63 { 64 int t,i,j,n,g; 65 cin>>t; 66 while(t--) 67 { 68 cin>>n; 69 for(i= 1; i <= n; i++) 70 { 71 scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i+n].x,&p[i+n].y); 72 } 73 if(n==1||n==2) 74 { 75 puts("Yes!"); 76 continue; 77 } 78 int flag = 0; 79 for(i = 1; i <= 2*n; i++) 80 { 81 for(j = i+1; j<= 2*n; j++) 82 { 83 line l1; 84 l1.a = p[i],l1.b = p[j]; 85 if(dcmp(dis(p[i]-p[j]))==0) continue; 86 int num = 0; 87 for(g = 1; g <= n ;g++) 88 { 89 if(Intersection(p[i],p[j],p[g],p[g+n])) num++; 90 else break; 91 } 92 if(num==n) 93 { 94 flag = 1; 95 break; 96 } 97 } 98 if(flag) break; 99 } 100 if(flag) puts("Yes!"); 101 else puts("No!"); 102 } 103 return 0; 104 }