POJ - 2240 Arbitrage(Bellman-Ford)

#include<cstdio>  
#include<cstring>  
#include<string>  
#include<algorithm>  
#include<iostream>  
#include<vector>  
#include<map>  
  
using namespace std;  
int n,m;  
double dist[40];    //注意类型为 double  
struct edge //边的结构体,st为起点,ed为终点,rt为汇率  
{  
    int st,ed;  
    double rt;  
    edge(int sst,int eed,double rtt) : st(sst),ed(eed),rt(rtt) {}  
    edge() {}  
};  
  
vector<edge> G;  
map<string ,int> mp;  
  
bool Bellman_ford(int v)  
{  
    memset(dist,0,sizeof(dist)); 
    dist[v] = 1;  
    for(int j = 1;j < n;j++) {  // n - 1 次松弛操作  
        for(int i = 0;i < G.size();i++) {  
            int p1 = G[i].st,p2 = G[i].ed;  
            if(dist[p2] < dist[p1] * G[i].rt) {
                dist[p2] = dist[p1] * G[i].rt;  
            }  
        }  
    }  
    for(int i = 0;i < G.size();i++){  
        int p1 = G[i].st,p2 = G[i].ed;  
        if(dist[p2] < dist[p1] * G[i].rt) { //第 n 次松弛可以得到更优解，则存在环  
            return true;      
        }  
    }  
    return false;  
}  
  
int main()  
{  
    int cas = 1;  
    string s,ss;  
    while(~scanf("%d",&n) &&n) {  
        for(int i = 0;i < n;i++) {  
            cin >> s;  
            mp[s] = i; //货币名 s 的顶点编号 为 i  
        }  
        cin >> m;  
        string beg,ends;  
        double r;  
        G.clear();  
        for(int i = 0;i < m;i++) {  
            cin >> beg >> r >> ends;    //边的信息读取  
            G.push_back(edge (mp[beg] ,mp[ends] ,r) );  
        }  
        printf("Case %d: ",cas++);  
        for(int i = 0;i < n;i++) { //枚举所有开始的起点  
            if(Bellman_ford(i)) {   //存在环  
                cout << "Yes" << endl;  
                //printf("bellman %d\n",i);  
                break;  
            }  
            else if(i == n - 1)  
                cout << "No" <<endl;  
        }  
    }  
    return 0;  
}