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。

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <map>
 4 #include <iomanip>
 5 #include <string>
 6 #include <cstring>
 7 #include <algorithm>
 8 using namespace std;
 9
10 const int MAXN=105;
11 const int MAXM=120000;
12 const int inf=90000000;
13 int head[MAXN];
14 struct e{
15     int u,v;
16     int depart,arrival;
17     int next;
18 }edge[MAXM];
19 int tot,n,m,limit;
20 int start_city,des_city;
21 string start,destin;
22 int timeh[105][2450];
23
24 void addedge(int u,int v,int de,int ar){
25     edge[tot].u=u;
26     edge[tot].v=v;
27     edge[tot].depart=de;
28     edge[tot].arrival=ar;
29     edge[tot].next=head[u];
30     head[u]=tot++;
31 }
32
33 void slove(){
34     for(int e=head[start_city];e!=-1;e=edge[e].next){
35         if(edge[e].depart>=limit){
36             timeh[edge[e].v][edge[e].arrival]=edge[e].depart;
37         }
38     }
39     for(int i=0;i<=2400;i++){
40         for(int j=1;j<=n;j++){
41             if(timeh[j][i]!=-1){
42                 for(int e=head[j];e!=-1;e=edge[e].next){
43                     if(i<=edge[e].depart){
44                         timeh[edge[e].v][edge[e].arrival]=max(timeh[edge[e].v][edge[e].arrival],timeh[j][i]);
45                     }
46                 }
47             }
48         }
49     }
50     for(int i=0;i<=2400;i++){
51         if(timeh[des_city][i]!=-1){
52             cout << "Departure " << setw(4) << setfill(‘0‘);
53             cout << timeh[des_city][i] << " " << start << endl;
54             cout << "Arrival   " << setw(4) << setfill(‘0‘);
55             cout << i << " " << destin << endl;
56             return ;
57         }
58     }
59     cout << "No connection" << endl;
60 }
61
62 int main(){
63     string station,pre,cur;
64     int cas=0;int T,pretime,curtime,u,v,train;
65     scanf("%d",&T);
66     while(T--){
67         cas++; tot=0;
68         memset(head,-1,sizeof(head));
69         memset(timeh,-1,sizeof(timeh));
70         map<string,int>city;
71         scanf("%d",&n);
72         for(int i=1;i<=n;i++){
73             cin>>station;
74             city[station]=i;
75         }
76         scanf("%d",&train);
77         while(train--){
78             scanf("%d",&m);
79             for(int i=1;i<=m;i++){
80                 cin>>curtime>>cur;
81                 if(i>1){
82                     u=city[pre];
83                     v=city[cur];
84                     addedge(u,v,pretime,curtime);
85                 }
86                 pre=cur;
87                 pretime=curtime;
88             }
89         }
90         cin>>limit>>start>>destin;
91         start_city=city[start]; des_city=city[destin];
92          cout << "Scenario " << cas << endl;
93         slove();
94         cout << endl;
95     }
96     return 0;
97 }

UVA 10039 Railroads