POJ1860---Currency Exchange

#include<iostream>
#include<string.h>
using namespace std;
const int maxn = 100+10;
struct node {
  int u,v;
  double r,c;//佣金:c 汇率r
} e[maxn * 2];
double dis[maxn],cnt;
int n,m,s,num,flag;
void add(int u,int v,double r,double c) {
  e[num].u = u;
  e[num].v= v;
  e[num].r = r;
  e[num].c = c;
  num++;
}
bool bellman_ford() {
  memset(dis,0,sizeof(dis));
  dis[s] = cnt;
  for(int i = 1; i  < n; i++) {
    flag = 0;
    for(int j = 0; j < num; j++) {
      if(dis[e[j].v] < (dis[e[j].u] - e[j].c)*e[j].r) {
        dis[e[j].v] = (dis[e[j].u] - e[j].c)*e[j].r;
        flag = 1;
      }
    }
    if(!flag) { //如果某一轮dis不再发生更新,则说明dis已更新完毕.
      return false;
    }
  }
  for(int j = 0; j < num; j++) {
    if(dis[e[j].v] < (dis[e[j].u] - e[j].c)*e[j].r) { //如果在第n次时还进行更新,则说明 出现了正环.
      return true;
    }
  }
  return false;
}
int main()
{
  cin>>n>>m>>s>>cnt;
  int u,v;
  double r1,c1,r2,c2;
  while(m--){
     cin>>u>>v>>c1>>r1>>c2>>r2; 
     add(u,v,c1,r1);
     add(v,u,c2,r2);
  }
  if(bellman_ford()){
    cout<<"YES"<<endl;
  }else{
    cout<<"NO"<<endl;
  }
  return 0;
}