poj 1860 Currency Exchange

#include <iostream>            //Bellman-Ford算法的变形,参照 poj 2240 Arbitrage
using namespace std;
const int maxnum = 102;
int n,m,s,a,b;
double v,r1,c1,r2,c2;
typedef struct Edge
{
    int u, v;    
    double ex,com;  
}Edge;

Edge edge[1000];     
double  dist[maxnum];     
int nodenum, edgenum; 

void input()
{
    cin>>n>>m>>s>>v;
    memset(dist,0,sizeof(dist));
    dist[s]=v;
    nodenum=n;edgenum=2*m;
    int i,j=1;
    for(i=1; i<=m; ++i)
    {
        cin>>a>>b>>r1>>c1>>r2>>c2;
        edge[j].u=a;
        edge[j].v=b;
        edge[j].ex=r1;edge[j++].com=c1;
        edge[j].u=b;
        edge[j].v=a;
        edge[j].ex=r2;edge[j++].com=c2;
    }
}
bool relax(int u, int v, double e,double c)
{
    if(dist[v] < (dist[u]-c) * e )        //这里是小于号
    {
        dist[v] = (dist[u]-c) * e ;
        return 1;
    }
    return 0;
}
bool Bellman_Ford()
{
    int tag=1;
    for(int i=1; i<=nodenum; ++i)
    {
        tag=1;
        for(int j=1; j<=edgenum; ++j)
            if(relax(edge[j].u, edge[j].v, edge[j].ex , edge[j].com))
                tag=0;
        if(tag==1)
            break;
    }
    // 判断是否有正权回路
    for(int i=1; i<=edgenum; ++i)
        if(dist[edge[i].v] < (dist[edge[i].u]-edge[i].com) * edge[i].ex)    //这里是小于号
            return 1;
    return 0;
}
int main()
{
    int t=1;
    int tag=0;
    input();
    if(Bellman_Ford())
        printf("YES\n");        
    else
        printf("NO\n");
    return 0;
}