Currency Exchange POJ - 1860

题意：币种兑换寻找是否有正环

计算公式 （money - Cost) * Rate

思路:spfa_dfs 判正环

#include<stdio.h>
#include<string.h>
#include <vector>
using namespace std;
const int MAX_V = 200;
struct edge {int to;
             double Rate,C;};
vector<edge> G[MAX_V];
bool instack[MAX_V];
double d[MAX_V];
int V;
bool spfa_dfs(int s){
  instack[s] = true;
  for (int i = 0;i<G[s].size();i++){
    edge e = G[s][i];
    if (d[e.to] < (d[s] -e.C) * e.Rate){
      d[e.to] = (d[s] - e.C) * e.Rate;
      if (!instack[e.to]){
        if (spfa_dfs(e.to)) return true;
      } else{
        return true;
      }

    }
  }
  instack[s] = false;
  return false;
}
int main()
{
  double money;
  int M,S;
  scanf("%d%d%d%lf",&V,&M,&S,&money);
  for (int i = 0;i<M;i++){
    int  u,v;
    double Ruv,Cuv,Rvu,Cvu;
    scanf("%d%d%lf%lf%lf%lf",&u,&v,&Ruv,&Cuv,&Rvu,&Cvu);
    G[u].push_back(edge{v,Ruv,Cuv});
    G[v].push_back(edge{u,Rvu,Cvu});
  }
  memset(d,0,sizeof d);
  memset(instack,0,sizeof instack);
  d[S] = money;
  if (spfa_dfs(S))
    printf("YES\n");
  else
    printf("NO\n");
  return 0;
}