Bellman-ford算法的反向应用－－正循环检查

/** \brief poj 1860 Bellman-Ford

 *

 * \param date 2014/7/24

 * \param state AC

 * \return memory 708K time 141ms

 *

 */

#include <iostream>

#include <fstream>

#include <cstring>

using namespace std;

struct RateAndCom

{

//public:

    int a;

    int b;

    double rate;

    double Com;

};//Map[MAXN];

const int MAXN=101;

RateAndCom Map[101*2];

double dis[MAXN];

int N;//货币种数

int M;//兑换点数量

int S;//持有第s种货币

double V;//第s种货币本金

int allEdge;

bool Bellman_Ford()

{

    memset(dis,0,sizeof(dis));

    dis[S]=V;

    /*relax*/

    bool flag;

    for(int i=1;i<=N-1;i++)

    {

        flag=false;

        for(int j=0;j<allEdge;j++)

            if(dis[Map[j].b] < (dis[Map[j].a]-Map[j].Com)*Map[j].rate)

        {

            dis[Map[j].b] = (dis[Map[j].a]-Map[j].Com)*Map[j].rate;

            flag=true;

        }

        if(!flag)

            break;

    }

    for(int k=0;k<allEdge;k++)

        if(dis[Map[k].b] < (dis[Map[k].a]-Map[k].Com)*Map[k].rate)

        return true;

    return false;

}

int main()

{

    //cout << "Hello world!" << endl;

    //freopen("input.txt","r",stdin);

    //while(scanf("%d %d %d %f",&N,&M,&S,&V)!=EOF)

    while(cin>>N>>M>>S>>V)

    {

        allEdge=0;

        for(int i=0;i<M;i++)

        {

            int a,b;

            double Rab;

            double Cab;

            double Rba;

            double Cba;

            //cin>>a>>b>>Map[a][b].rate>>Map[a][b].Commission

            //>>Map[b][a].rate>>Map[b][a].Commission;

            cin>>a>>b>>Rab>>Cab>>Rba>>Cba;

            Map[allEdge].a=a;

            Map[allEdge].b=b;

            Map[allEdge].rate=Rab;

            Map[allEdge].Com=Cab;

            allEdge++;

            Map[allEdge].a=b;

            Map[allEdge].b=a;

            Map[allEdge].rate=Rba;

            Map[allEdge].Com=Cba;

            allEdge++;

        }

        //Bellman-Ford

        if(Bellman_Ford())

            cout<<"YES"<<endl;

        else cout<<"NO"<<endl;

    }

    return 0;

}

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