SPFA

int SPFA(){     int i,temp;     deque<int>Q;     bool flag[1001];//是否在队列中      int dist[1001];     memset(dist,63,sizeof(dist));     memset(flag,0,sizeof(flag));     flag[1]=1;     Q.push_back(1);     dist[1]=0;     while(!Q.empty())     {        temp=Q.at(0);        Q.pop_front();        for(i=1;i<=N;i++)        {            if(dist[i]>dist[temp]+map[temp][i])            {                dist[i]=dist[temp]+map[temp][i];                if(flag[i]==0)                {                    flag[i]=1;                    Q.push_back(i);                }            }        }        flag[temp]=0;     }     return dist[N];}

+上进队次数可以判负环