poj-------(2240)Arbitrage(最短路)

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<string>
 5 #include<iostream>
 6 #include<map>
 7 #include<iterator>
 8 using namespace std;
 9 const double inf =-100;
10 const int maxn = 105;
11 struct node
12 {
13  int u,v;
14  double val;
15 };
16 node edge[1000];
17 double dist[maxn];
18 /*松弛状态判别*/
19 bool relax(int u,int v,double val){
20     if(dist[v]<dist[u]*val){
21         dist[v]=dist[u]*val;
22         return 1;
23     }
24     return 0;
25 }
26 bool Bellman(int st,int n,int m){
27     for(int i=1;i<=n;i++){    //初始化
28         dist[i]=inf;
29     }
30     dist[st]=1;
31     bool flag;
32     /*循环优化部分*/
33     for(int i=1; i<n;i++) {
34           flag=false;
35       for(int j=1;j<=m;j++){
36          if(relax(edge[j].u,edge[j].v,edge[j].val))
37              flag=true;
38          }
39        if(!flag) break;
40     }
41     /*检验部分*/
42     for(int i=1;i<=m;i++){
43        if(relax(edge[i].u,edge[i].v,edge[i].val))
44           return 1;   //有负圈
45     }
46     return 0;
47 }
48 
49 int main()
50 {
51     int n,m;
52     map<string ,int> sac;
53     string temp;
54     int test=1;
55     while(scanf("%d",&n)==1&&n!=0){
56             if(!sac.empty())sac.clear();
57         for(int i=1;i<=n;i++){
58            cin>>temp;
59         // sac.insert(pair<string ,int>(temp,i));
60            sac[temp]=i;
61         }
62          cin>>m;
63          double ss;
64          string aa,bb;
65         map<string,int>::iterator p1,p2;
66         for(int i=1 ; i<=m ; i++ ){
67            cin>>aa>>ss>>bb;
68            p1=sac.find(aa);
69            p2=sac.find(bb);
70            edge[i].u=p1->second;
71            edge[i].v=p2->second;
72            edge[i].val=ss;
73         }
74 
75         if(Bellman(1,n,m)) printf("Case %d: Yes\n",test);
76            else printf("Case %d: No\n",test);
77         test++;
78         // printf("%lf\n",dist[1]);
79     }
80     return 0;
81 }