POJ 1860 Currency Exchange 毫无优化的bellman_ford跑了16Ms，spfa老是WA。。

题目链接： http://poj.org/problem?id=1860

找正环，找最长路，水题，WA了两天了。。

#include <stdio.h>
#include <string.h>

struct Edge
{
    int u, v;
    double r, c;
}edge[210];

int rear, n, m, s;
double v, dist[110];

bool bellman_ford()
{
    memset(dist, 0, sizeof(dist));
    dist[s] = v;
    for(int i = 1; i < n; i++)
        for(int j = 0; j < rear; j++)
            if(dist[edge[j].v] < (dist[edge[j].u]-edge[j].c) * edge[j].r)
                dist[edge[j].v] = (dist[edge[j].u]-edge[j].c) * edge[j].r;

    for(int j = 0; j < rear; j++)
        if(dist[edge[j].v] < (dist[edge[j].u]-edge[j].c) * edge[j].r)
            return 1;
    return 0;
}

int main()
{
    int a, b;
    double rab, cab, rba, cba;
    while(scanf("%d %d %d %lf", &n, &m, &s, &v) != EOF)
    {
        rear = 0;
        while(m--)
        {
            scanf("%d %d %lf %lf %lf %lf", &a, &b, &rab, &cab, &rba, &cba);
            edge[rear++] = (struct Edge){a, b, rab, cab};
            edge[rear++] = (struct Edge){b, a, rba, cba};
        }
        printf("%s\n", bellman_ford() ? "YES" : "NO");
    }
    return 0;
}