poj 3304 找一条直线穿过所有线段
题目链接:http://poj.org/problem?id=3304
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#include<cstdio> #include<cstring> #include<cmath> #include<iostream> #include<algorithm> #include<queue> using namespace std; const int maxn = 105; const int maxe = 20000; const int INF = 0x3f3f3f; const double eps = 1e-8; const double PI = acos(-1.0); struct Point{ double x,y; Point(double x=0, double y=0) : x(x),y(y){ } //构造函数 }; typedef Point Vector; Vector operator + (Vector A , Vector B){return Vector(A.x+B.x,A.y+B.y);} Vector operator - (Vector A , Vector B){return Vector(A.x-B.x,A.y-B.y);} Vector operator * (Vector A , double p){return Vector(A.x*p,A.y*p);} Vector operator / (Vector A , double p){return Vector(A.x/p,A.y/p);} bool operator < (const Point& a,const Point& b){ return a.x < b.x ||( a.x == b.x && a.y < b.y); } int dcmp(double x){ if(fabs(x) < eps) return 0; else return x < 0 ? -1 : 1; } bool operator == (const Point& a, const Point& b){ return dcmp(a.x - b.x) == 0 && dcmp(a.y - b.y) == 0; } double Dot(Vector A, Vector B){ return A.x*B.x + A.y*B.y; } double Cross(Vector A, Vector B) { return A.x*B.y - A.y * B.x; } double Length(Vector A) { return sqrt(Dot(A,A)); } bool SegmentLineIntersection(Point a1,Point a2,Point b1,Point b2){ //a1a2是直线,b1b2是线段; double c1 = Cross(a2-a1,b1-a1), c2 = Cross(a2-a1,b2-a1); return dcmp(c1) * dcmp(c2) < 0 || dcmp(c1) == 0 || dcmp(c2) == 0; } Point read_point(){ Point A; scanf("%lf %lf",&A.x,&A.y); return A; } /******************************分割线*******************************/ Point P[maxn][2]; int n; int main() { //freopen("E:\\acm\\input.txt","r",stdin); int T; cin>>T; while(T--){ cin>>n; for(int i=1;i<=n;i++){ P[i][0] = read_point(); P[i][1] = read_point(); } bool ans = false; for(int i=1;i<n;i++) for(int k=0;k<=1;k++) for(int j=i+1;j<=n;j++) for(int m=0;m<=1;m++){ //确定两个端点P[i][k]和P[j][m];接下来判断过这两点直线是否穿过所有线段; if(P[i][k] == P[j][m]) continue; int s; for(s=1;s<=n;s++){ if(!SegmentLineIntersection(P[i][k],P[j][m],P[s][0],P[s][1])) break; } if(s == n+1) { ans = true; goto print; } } print: if(ans || n==1) printf("Yes!\n"); //n == 1没考虑,WA了两次看discuss别人说的; else printf("No!\n"); } }