Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 17374		Accepted: 7312

Arbitrage is the use of discrepancies in currency exchange rates to transform one unit of a currency into more than one unit of the same currency. For example, suppose that 1 US Dollar buys 0.5 British pound, 1 British pound buys 10.0 French francs, and 1 French franc buys 0.21 US dollar. Then, by converting currencies, a clever trader can start with 1 US dollar and buy 0.5 * 10.0 * 0.21 = 1.05 US dollars, making a profit of 5 percent.

Your job is to write a program that takes a list of currency exchange rates as input and then determines whether arbitrage is possible or not.

The input will contain one or more test cases. Om the first line of each test case there is an integer n (1<=n<=30), representing the number of different currencies. The next n lines each contain the name of one currency. Within a name no spaces will appear. The next line contains one integer m, representing the length of the table to follow. The last m lines each contain the name ci of a source currency, a real number rij which represents the exchange rate from ci to cj and a name cj of the destination currency. Exchanges which do not appear in the table are impossible. 
Test cases are separated from each other by a blank line. Input is terminated by a value of zero (0) for n.

For each test case, print one line telling whether arbitrage is possible or not in the format "Case case: Yes" respectively "Case case: No".

3

USDollar

BritishPound

FrenchFranc

3

USDollar 0.5 BritishPound

BritishPound 10.0 FrenchFranc

FrenchFranc 0.21 USDollar

3

USDollar

BritishPound

FrenchFranc

6

USDollar 0.5 BritishPound

USDollar 4.9 FrenchFranc

BritishPound 10.0 FrenchFranc

BritishPound 1.99 USDollar

FrenchFranc 0.09 BritishPound

FrenchFranc 0.19 USDollar

0

Case 1: Yes

Case 2: No
这题较简单，使用bellman-ford算法就可以了，注意输出，我因为输出WA几次

 #include <iostream>

 #include<map>

 #include<string.h>

 using namespace std;

 struct edge{

     int u,v;

     float rate;

 } e[*];

 int cur_num,edge_num;

 float dis[];

 map<string,int> mp;

 int Bellman_ford(int c){

     memset(dis,,*sizeof(float));

     dis[c]=1.0;

     for(int i=;i<cur_num;i++){

         for(int j=;j<edge_num;j++){

             if(dis[e[j].v]<dis[e[j].u]*e[j].rate){

                 dis[e[j].v]=dis[e[j].u]*e[j].rate;

             }

         }

     }

     if(dis[c]>1.0)

         return ;

     else

         return ;

 }

 int main() {

     int count=;

     cin>>cur_num;

     while(cur_num){

         mp.clear();

         for(int i=;i<cur_num;i++){

             string s;

             cin>>s;

             mp[s]=i;

         }

         cin>>edge_num;

         for(int i=;i<edge_num;i++){

             string s1,s2;

             float rate;

             cin>>s1>>rate>>s2;

             e[i].u=mp[s1];

             e[i].v=mp[s2];

             e[i].rate=rate;

         }

         int flag=;

         for(int i=;i<cur_num;i++){

             flag=Bellman_ford(i);

             if(flag)

                 break;

         }

         if(flag)

             cout<<"Case "<<++count<<": Yes"<<endl;

         else

             cout<<"Case "<<++count<<": No"<<endl;

         cin>>cur_num;

     }

     return ;

 }