poj 3259 Wormholes

这是一道求有没有负环的题，用到bellman算法；

这里要注意的是路是双向的；

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
using namespace std;
class Weight
{
public:
      int S,E,T;
}edge[5024];
bool Bell_man( int count, int N )
{
    int dis[1024] = {0},flag = 0;
    for( int i = 0 ; i < N -1 ; i ++ )
    {
        flag = 0;
           for( int j = 0 ; j < count; j ++ )
           {
            if( dis[edge[j].E] > dis[edge[j].S] + edge[j].T )
            {
                dis[edge[j].E] = dis[edge[j].S] + edge[j].T;    
                flag = 1;
            }        
        }
        if( !flag ) break;
    }    
    for( int i = 0 ; i < count ; i ++ )
    {
       if( dis[edge[i].E] > dis[edge[i].S] + edge[i].T )
         return true;       
    }
    return false;
}
int main()
{
    int Case,N,M,W,S,T,E;
    while( scanf( "%d",&Case )==1 )
    {
       while( Case-- )
       {
          int count = 0;
          scanf( "%d %d %d",&N,&M,&W );
          for( int i = 0 ; i < M; i ++ )
          {
               scanf( "%d %d %d",&S,&E,&T );
               edge[count].S = edge[count+1].E = S;
               edge[count+1].S = edge[count].E = E;
               edge[count].T = edge[count+1].T = T; count+=2;        
          }        
          for( int i = 0 ; i < W ; i ++ )
          {
              scanf( "%d %d %d",&S,&E,&T );
              edge[count].S = S ; edge[count].E= E;
              edge[count].T = -T ; count++;        
          }
          if( Bell_man( count ,N ) )
             printf( "YES\n" );
          else printf( "NO\n" );
       }    
    }
   return 0;    
}