POJ1860(Bellman-Ford思想)


#include <iostream>
#include <cstdio>
#include <map>
#include <cstring>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;

struct edge
{
	int s,e;
	double commission;
	double rate;
};

int main()
{
  int n,m,s;
  double v;
  int i,j;
  struct edge e[205];
  double d[105]={0};

  scanf("%d%d%d%lf",&n,&m,&s,&v);
  for (i=0;i<m;i++)
  {
  	int a,b;
  	double Rab,Cab,Rba,Cba;
  	scanf("%d%d%lf%lf%lf%lf",&a,&b,&Rab,&Cab,&Rba,&Cba);
  	e[i].s=a;
  	e[i].e=b;
  	e[i].commission=Cab;
  	e[i].rate=Rab;
  	e[i+m].s=b;
  	e[i+m].e=a;
  	e[i+m].commission=Cba;
  	e[i+m].rate=Rba;
  }

  bool flag=false;
  d[s]=v;
  for (i=0;i<n;i++)
  	for (j=0;j<2*m;j++)
  	{
  		if ( (d[e[j].s]-e[j].commission)*e[j].rate > d[e[j].e] )
  		{
  			d[e[j].e]=(d[e[j].s]-e[j].commission)*e[j].rate;
  			if (i==n-1) flag=true;
  		}
  	}

  if (flag) printf("YES\n");
  else printf("NO\n");
}


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