Currency Exchange POJ 1860

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<algorithm>
#include<queue>
using namespace std;
typedef long long LL;
#define oo 0x3f3f3f3f
#define maxn 310
int head[maxn], num[maxn], v[maxn];
double dist[maxn];
int n, s, cnt;
double V;

struct node
{
    int v, next;
    double r, c;
}e[maxn];

void Add(int u, int v, double r, double c)
{
    e[cnt].v=v;
    e[cnt].r=r;
    e[cnt].c=c;
    e[cnt].next=head[u];
    head[u]=cnt++;
}

int spfa()
{
   queue<int>Q;
   v[s] = 1;
   num[s]++;
   dist[s] = V;
   Q.push(s);

   while(Q.size())
   {
       int p = Q.front();
       Q.pop();
       v[p] = 0;

       for(int i=head[p]; i!=-1; i=e[i].next)
       {
           int q = e[i].v;
           double k = (dist[p] - e[i].c)*e[i].r;
           if(dist[q] < k)
           {
               dist[q] = k;
               if(!v[q])
               {
                   v[q] = 1;
                   num[q]++;
                   Q.push(q);
                   if(num[q]>n) return 1;
               }
           }
       }
   }

   if(dist[s] > V) return 1;

   return 0;
}

int main()
{
    int a, b, m;
    double rab, rba, cab, cba;
    while(scanf("%d%d%d%lf", &n, &m, &s, &V)!=EOF)
    {
        cnt = 0;
        memset(head, -1, sizeof(head));
        memset(dist, 0, sizeof(dist));
        memset(v, 0, sizeof(v));
        memset(num, 0, sizeof(num));

        for(int i=1; i<=m; i++)
        {
            scanf("%d%d%lf%lf%lf%lf", &a, &b, &rab, &cab, &rba, &cba);
            Add(a, b, rab, cab);
            Add(b, a, rba, cba);
        }

        if( spfa() )
            printf("YES\n");
        else
            printf("NO\n");
    }
    return 0;
}