POJ 2240 Arbitrage (最短路)

 1 #include <iostream>
 2 #include <string>
 3 #include <map>
 4 #include <vector>
 5 #include <queue>
 6 #include <cstdio>
 7 using    namespace    std;
 8 
 9 const    int    INF = 0xffffff;
10 const    int    SIZE = 35;
11 int    N,M;
12 double    D[SIZE];
13 struct    Node
14 {
15     int    from,to;
16     double    cost;
17 }G[1000];
18 map<string,int>    mapstring;
19 
20 bool    Bellman_Ford(int);
21 bool    relax(int,int,double);
22 int    main(void)
23 {
24     string    box,box_2;
25     double    num;
26     int    from,to;
27     int    count = 0;
28 
29     while(scanf("%d",&N) && N)
30     {
31         count ++;
32         for(int i = 1;i <= N;i ++)
33         {
34             cin >> box;
35             mapstring.insert(pair<string,int>(box,i));
36         }
37         scanf("%d",&M);
38         for(int i = 0;i < M;i ++)
39         {
40             cin >> box >> num >> box_2;
41             G[i].from = mapstring[box];
42             G[i].to = mapstring[box_2];
43             G[i].cost = num;
44         }
45         bool    flag = true;
46         for(int i = 1;i <= N;i ++)
47             if(!Bellman_Ford(i))
48             {
49                 printf("Case %d: Yes\n",count);
50                 flag = false;
51                 break;
52             }
53         if(flag)
54             printf("Case %d: No\n",count);
55     }
56 
57     return    0;
58 }
59 
60 bool    Bellman_Ford(int s)
61 {
62     bool    update;
63     fill(D,D + SIZE,0);
64     D[s] = INF;
65 
66     for(int i = 0;i < N - 1;i ++)
67     {
68         update = false;
69         for(int j = 0;j < M;j ++)
70             if(relax(G[j].from,G[j].to,G[j].cost))
71                 update = true;
72         if(!update)
73             break;
74     }
75     for(int i = 0;i < M;i ++)
76         if(relax(G[i].from,G[i].to,G[i].cost))
77             return    false;
78 
79     return    true;
80 }
81 
82 bool    relax(int from,int to,double cost)
83 {
84     if(D[to] < D[from] * cost)
85     {
86         D[to] = D[from] * cost;
87         return    true;
88     }
89     return    false;
90 }