PKU1860--Currency Exchange

本题需要注意的是，起点不一定是从1开始，在初始化的时候也需注意。

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <string.h>
#include <math.h>
#define Min(a,b) a<b?a:b
#define Max(a,b) a<b?b:a
#define M 105*5
#define INF 999999999
using namespace std;

int n,m;
int k,s;
double dis[M];
double v;

struct Edge
{
int from,to;
double R;
double C;
};
struct Edge edge[M];

bool Bellman_Ford()
{
int i,j;
for(i=1;i<M;i++)
{
dis[i]=0;
}
dis[s]=v;
bool flag;
for(i=1;i<n;i++)
{
flag=false;
for(j=1;j<=k;j++)
{
if(dis[edge[j].to]<(dis[edge[j].from]-edge[j].C)*edge[j].R)
{
dis[edge[j].to]=(dis[edge[j].from]-edge[j].C)*edge[j].R;
flag=true;
}
}
if(!flag)
break;
}
for(j=1;j<=k;j++)
{
if(dis[edge[j].to]<(dis[edge[j].from]-edge[j].C)*edge[j].R)
return true;
}
return false;
}

int main()
{
int i;
while(scanf("%d%d%d%lf",&n,&m,&s,&v)!=EOF)
{
k=1;
for(i=0;i<m;i++)
{
int a,b;
double Rab,Rba,Cab,Cba;
scanf("%d%d%lf%lf%lf%lf",&a,&b,&Rab,&Cab,&Rba,&Cba);
edge[k].from=a,edge[k].to=b,edge[k].R=Rab,edge[k++].C=Cab;
edge[k].from=b,edge[k].to=a,edge[k].R=Rba,edge[k++].C=Cba;
}
if(Bellman_Ford())
printf("YES\n");
else
printf("NO\n");
}
return 0;
}