BellmanFord模版

 

 

struct Edge{
    int from,to;
    int dist;
};
struct BellmanFord{
    int n,m;
    vector<Edge>edges;
    vector<int>G[MAXN];
    bool inq[MAXN];
    int d[MAXN];
    int p[MAXN];
    int cnt[MAXN];
    void init(int n)
    {
        this->n=n;
        for(int i=0;i<n;i++)G[i].clear();
        edges.clear();
    }
    void AddEdge(int from,int to,int dist)
    {
        edges.push_back((Edge){from,to,dist});
        m=edges.size();
        G[from].push_back(m-1);
    }
    bool negativeCycle()
    {
        queue<int>Q;
        memset(inq,0,sizeof(inq));
        memset(cnt,0,sizeof(cnt));
        for(int i=0;i<n;i++)
        {
        d[i]=0;inq[0]=true;Q.push(i);
        }
        while(!Q.empty())
        {
            int u=Q.front();Q.pop();
            inq[u]=false;
            for(int i=0;i<G[u].size();i++)
            {
                Edge& e=edges[G[u][i]];
                if(d[e.to]>d[u]+e.dist)
                {
                    d[e.to]=d[u]+e.dist;
                    p[e.to]=G[u][i];
                    if(!inq[e.to])
                    {
                        Q.push(e.to);
                        inq[e.to]=true;
                        if(++cnt[e.to]>n)
                            return true;
                    }
                }
            }
        }
        return false;
    }
};