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-8;
const db pi=acos(-1);
int sign(db k){
    if (k>eps) return 1; else if (k<-eps) return -1; return 0;
}
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)!=-1&&cmp(r2,l1)!=-1;
}
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))<0&&
           sign(cross(k1-k3,k2-k3))*sign(cross(k1-k4,k2-k4))<0;
}
struct line{
    point p[2];
};
int checkSS(line a,line b){
    return checkSS(a.p[0],a.p[1],b.p[0],b.p[1]);
}
int n;
db dis[100010];
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[500010];
int head[100010],cnt=0;
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=1;i<=10000;i++) dis[i]=10000;
    dis[0]=0;
    priority_queue<node> Q; //堆
    Q.push((node){0,0});
    while (!Q.empty()) {
        node fr=Q.top(); Q.pop();
        int u=fr.u;db d=fr.d;
        if (cmp(d,dis[u])>0) 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])<0) {
                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=0;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(2);
    while (cin>>n&&n!=-1){
        g.push_back(point{0,5});
        for(int i=1;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,0},point{x,yl}});
            v.push_back(line{point{x,y2},point{x,y3}});
            v.push_back(line{point{x,y4},point{x,10}});
        }
        g.push_back(point{10,5});
        int m=g.size();
        for(int i=0;i<m;i++){
            for(int j=i+1;j<m;j++){
                if(check(line{g[i],g[j]})){
                    //printf("%d %d
",i,j);
                    addEdge(i,j,g[i].dis(g[j]));
                    addEdge(j,i,g[i].dis(g[j]));
                }
            }
        }
        Dijkstra();
        cout<<dis[m-1]<<endl;
        g.clear();
        v.clear();
        cnt=0;
        memset(head,0, sizeof(head));
    }
}
/**
2
4 2 7 8 9
7 3 4.5 6 7
-1
 */