UVA 10039 Railroads

这道题好吧，一开始便是拓扑排序的想法，搞了好久，试了多组测试数据，没错啊，可是没过。。。作孽啊，竟然忘了拓扑不能处理环，白浪费了一晚上。。。

只好用动态规划了。。

DP【time】【city】表示在time时刻到达city的最迟出发时间，当然，在这个时间不一定到city。

转移方程挺简单，不说你也会。

 #include <iostream>
 #include <cstdio>
 #include <map>
 #include <iomanip>
 #include <string>
 #include <cstring>
 #include <algorithm>
 using namespace std;

 const int MAXN=;
 const int MAXM=;
 const int inf=;
 int head[MAXN];
 struct e{
     int u,v;
     int depart,arrival;
     int next;
 }edge[MAXM];
 int tot,n,m,limit;
 int start_city,des_city;
 string start,destin;
 int timeh[][];

 void addedge(int u,int v,int de,int ar){
     edge[tot].u=u;
     edge[tot].v=v;
     edge[tot].depart=de;
     edge[tot].arrival=ar;
     edge[tot].next=head[u];
     head[u]=tot++;
 }

 void slove(){
     for(int e=head[start_city];e!=-;e=edge[e].next){
         if(edge[e].depart>=limit){
             timeh[edge[e].v][edge[e].arrival]=edge[e].depart;
         }
     }
     for(int i=;i<=;i++){
         for(int j=;j<=n;j++){
             if(timeh[j][i]!=-){
                 for(int e=head[j];e!=-;e=edge[e].next){
                     if(i<=edge[e].depart){
                         timeh[edge[e].v][edge[e].arrival]=max(timeh[edge[e].v][edge[e].arrival],timeh[j][i]);
                     }
                 }
             }
         }
     }
     for(int i=;i<=;i++){
         if(timeh[des_city][i]!=-){
             cout << "Departure " << setw() << setfill('');
             cout << timeh[des_city][i] << " " << start << endl;
             cout << "Arrival   " << setw() << setfill('');
             cout << i << " " << destin << endl;
             return ;
         }
     }
     cout << "No connection" << endl;
 }

 int main(){
     string station,pre,cur;
     int cas=;int T,pretime,curtime,u,v,train;
     scanf("%d",&T);
     while(T--){
         cas++; tot=;
         memset(head,-,sizeof(head));
         memset(timeh,-,sizeof(timeh));
         map<string,int>city;
         scanf("%d",&n);
         for(int i=;i<=n;i++){
             cin>>station;
             city[station]=i;
         }
         scanf("%d",&train);
         while(train--){
             scanf("%d",&m);
             for(int i=;i<=m;i++){
                 cin>>curtime>>cur;
                 if(i>){
                     u=city[pre];
                     v=city[cur];
                     addedge(u,v,pretime,curtime);
                 }
                 pre=cur;
                 pretime=curtime;
             }
         }
         cin>>limit>>start>>destin;
         start_city=city[start]; des_city=city[destin];
          cout << "Scenario " << cas << endl;
         slove();
         cout << endl;
     }
     return ;
 }