poj 1556

哦天哪这个萨比提又浪费了我好几个小时。

我们在check的时候只考虑严格相交就行了，想了很久才注意到这一点。

然后就建图跑最短路，over。

 #include <cstdio>
 #include <cmath>
 #include <algorithm>
 #include <vector>
 #include <queue>
 #include <cstring>
 #include <iomanip>
 #include <iostream>
 typedef double db;
 using namespace std;
 const db eps=1e-;
 const db pi=acos(-);
 int sign(db k){
     if (k>eps) return ; else if (k<-eps) return -; return ;
 }
 int cmp(db k1,db k2){return sign(k1-k2);}
 struct point{
     db x,y;
     point operator + (const point &k1) const{return (point){k1.x+x,k1.y+y};}
     point operator - (const point &k1) const{return (point){x-k1.x,y-k1.y};}
     point operator * (db k1) const{return (point){x*k1,y*k1};}
     point operator / (db k1) const{return (point){x/k1,y/k1};}
     db abs(){ return sqrt(x*x+y*y);}
     db dis(point k1){ return(*this-k1).abs();}
 };
 db cross(point k1,point k2){ return k1.x*k2.y-k1.y*k2.x; }
 db dot(point k1,point k2){ return k1.x*k2.x+k1.y*k2.y;}
 int intersect(db l1,db r1,db l2,db r2){
     if (l1>r1) swap(l1,r1); if (l2>r2) swap(l2,r2); return cmp(r1,l2)!=-&&cmp(r2,l1)!=-;
 }
 int checkSS(point k1,point k2,point k3,point k4){
     return //intersect(k1.x,k2.x,k3.x,k4.x)&&intersect(k1.y,k2.y,k3.y,k4.y)&&
            sign(cross(k3-k1,k4-k1))*sign(cross(k3-k2,k4-k2))<&&
            sign(cross(k1-k3,k2-k3))*sign(cross(k1-k4,k2-k4))<;
 }
 struct line{
     point p[];
 };
 int checkSS(line a,line b){
     return checkSS(a.p[],a.p[],b.p[],b.p[]);
 }
 int n;
 db dis[];
 struct node { //堆节点
     int u;db d;
     bool operator <(const node& rhs) const {
         return d>rhs.d;
     }
 };
 struct Edge { int v,nxt;db w;};
 Edge e[];
 int head[],cnt=;
 void addEdge(int u,int v,db w) {
     e[++cnt].v=v;
     e[cnt].w=w;
     e[cnt].nxt=head[u];
     head[u]=cnt;
 }
 void Dijkstra() {
     for (int i=;i<=;i++) dis[i]=;
     dis[]=;
     priority_queue<node> Q; //堆
     Q.push((node){,});
     while (!Q.empty()) {
         node fr=Q.top(); Q.pop();
         int u=fr.u;db d=fr.d;
         if (cmp(d,dis[u])>) continue;
         for (int i=head[u];i;i=e[i].nxt) {
             int v=e[i].v;db w=e[i].w;
             if (cmp(dis[u]+w,dis[v])<) {
                 dis[v]=dis[u]+w;
                 Q.push((node){v,dis[v]});
             }
         }
     }
 }
 db yl,y2,y3,y4,x;
 vector<line> v;
 vector<point> g;
 bool check(line tmp){
     for(int i=;i<v.size();i++){
         if(checkSS(tmp,v[i])){
             return false;
         }//return false;
     }
     return true;
 }
 int main(){
     ios::sync_with_stdio(false);
     cout<<fixed<<setprecision();
     while (cin>>n&&n!=-){
         g.push_back(point{,});
         for(int i=;i<=n;i++){
             cin>>x>>yl>>y2>>y3>>y4;
             g.push_back(point{x,yl});
             g.push_back(point{x,y2});
             g.push_back(point{x,y3});
             g.push_back(point{x,y4});
             v.push_back(line{point{x,},point{x,yl}});
             v.push_back(line{point{x,y2},point{x,y3}});
             v.push_back(line{point{x,y4},point{x,}});
         }
         g.push_back(point{,});
         int m=g.size();
         for(int i=;i<m;i++){
             for(int j=i+;j<m;j++){
                 if(check(line{g[i],g[j]})){
                     //printf("%d %d\n",i,j);
                     addEdge(i,j,g[i].dis(g[j]));
                     addEdge(j,i,g[i].dis(g[j]));
                 }
             }
         }
         Dijkstra();
         cout<<dis[m-]<<endl;
         g.clear();
         v.clear();
         cnt=;
         memset(head,, sizeof(head));
     }
 }
 /**
 2
 4 2 7 8 9
 7 3 4.5 6 7
 -1
  */