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。

  1 #include <cstdio>
  2 #include <cmath>
  3 #include <algorithm>
  4 #include <vector>
  5 #include <queue>
  6 #include <cstring>
  7 #include <iomanip>
  8 #include <iostream>
  9 typedef double db;
 10 using namespace std;
 11 const db eps=1e-8;
 12 const db pi=acos(-1);
 13 int sign(db k){
 14     if (k>eps) return 1; else if (k<-eps) return -1; return 0;
 15 }
 16 int cmp(db k1,db k2){return sign(k1-k2);}
 17 struct point{
 18     db x,y;
 19     point operator + (const point &k1) const{return (point){k1.x+x,k1.y+y};}
 20     point operator - (const point &k1) const{return (point){x-k1.x,y-k1.y};}
 21     point operator * (db k1) const{return (point){x*k1,y*k1};}
 22     point operator / (db k1) const{return (point){x/k1,y/k1};}
 23     db abs(){ return sqrt(x*x+y*y);}
 24     db dis(point k1){ return(*this-k1).abs();}
 25 };
 26 db cross(point k1,point k2){ return k1.x*k2.y-k1.y*k2.x; }
 27 db dot(point k1,point k2){ return k1.x*k2.x+k1.y*k2.y;}
 28 int intersect(db l1,db r1,db l2,db r2){
 29     if (l1>r1) swap(l1,r1); if (l2>r2) swap(l2,r2); return cmp(r1,l2)!=-1&&cmp(r2,l1)!=-1;
 30 }
 31 int checkSS(point k1,point k2,point k3,point k4){
 32     return //intersect(k1.x,k2.x,k3.x,k4.x)&&intersect(k1.y,k2.y,k3.y,k4.y)&&
 33            sign(cross(k3-k1,k4-k1))*sign(cross(k3-k2,k4-k2))<0&&
 34            sign(cross(k1-k3,k2-k3))*sign(cross(k1-k4,k2-k4))<0;
 35 }
 36 struct line{
 37     point p[2];
 38 };
 39 int checkSS(line a,line b){
 40     return checkSS(a.p[0],a.p[1],b.p[0],b.p[1]);
 41 }
 42 int n;
 43 db dis[100010];
 44 struct node { //堆节点
 45     int u;db d;
 46     bool operator <(const node& rhs) const {
 47         return d>rhs.d;
 48     }
 49 };
 50 struct Edge { int v,nxt;db w;};
 51 Edge e[500010];
 52 int head[100010],cnt=0;
 53 void addEdge(int u,int v,db w) {
 54     e[++cnt].v=v;
 55     e[cnt].w=w;
 56     e[cnt].nxt=head[u];
 57     head[u]=cnt;
 58 }
 59 void Dijkstra() {
 60     for (int i=1;i<=10000;i++) dis[i]=10000;
 61     dis[0]=0;
 62     priority_queue<node> Q; //堆
 63     Q.push((node){0,0});
 64     while (!Q.empty()) {
 65         node fr=Q.top(); Q.pop();
 66         int u=fr.u;db d=fr.d;
 67         if (cmp(d,dis[u])>0) continue;
 68         for (int i=head[u];i;i=e[i].nxt) {
 69             int v=e[i].v;db w=e[i].w;
 70             if (cmp(dis[u]+w,dis[v])<0) {
 71                 dis[v]=dis[u]+w;
 72                 Q.push((node){v,dis[v]});
 73             }
 74         }
 75     }
 76 }
 77 db yl,y2,y3,y4,x;
 78 vector<line> v;
 79 vector<point> g;
 80 bool check(line tmp){
 81     for(int i=0;i<v.size();i++){
 82         if(checkSS(tmp,v[i])){
 83             return false;
 84         }//return false;
 85     }
 86     return true;
 87 }
 88 int main(){
 89     ios::sync_with_stdio(false);
 90     cout<<fixed<<setprecision(2);
 91     while (cin>>n&&n!=-1){
 92         g.push_back(point{0,5});
 93         for(int i=1;i<=n;i++){
 94             cin>>x>>yl>>y2>>y3>>y4;
 95             g.push_back(point{x,yl});
 96             g.push_back(point{x,y2});
 97             g.push_back(point{x,y3});
 98             g.push_back(point{x,y4});
 99             v.push_back(line{point{x,0},point{x,yl}});
100             v.push_back(line{point{x,y2},point{x,y3}});
101             v.push_back(line{point{x,y4},point{x,10}});
102         }
103         g.push_back(point{10,5});
104         int m=g.size();
105         for(int i=0;i<m;i++){
106             for(int j=i+1;j<m;j++){
107                 if(check(line{g[i],g[j]})){
108                     //printf("%d %d\n",i,j);
109                     addEdge(i,j,g[i].dis(g[j]));
110                     addEdge(j,i,g[i].dis(g[j]));
111                 }
112             }
113         }
114         Dijkstra();
115         cout<<dis[m-1]<<endl;
116         g.clear();
117         v.clear();
118         cnt=0;
119         memset(head,0, sizeof(head));
120     }
121 }
122 /**
123 2
124 4 2 7 8 9
125 7 3 4.5 6 7
126 -1
127  */

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