最小费用流模版

const int M=20010,ME=500000;
const int INF=0x3f3fffff;
//******************************
int Head[M],Next[ME],Num[ME],Flow[ME],Cap[ME],Cost[ME],Q[M],InQ[M],Len[M],pre_edge[M];
class MaxFlow
{
public:
    void clear()
    {
		memset(Head,-1,sizeof(Head));
		memset(Flow,0,sizeof(Flow));
    }
    void addedge(int u,int v,int cap,int cost)
    {
        Next[top] = Head[u];
        Num[top] = v;
        Cap[top] = cap;
        Cost[top] = cost;
        Head[u] = top++;
 
        Next[top] = Head[v];
        Num[top] = u;
        Cap[top] = 0;
        Cost[top] = -cost;
        Head[v] = top++;
    }
    int solve(int s,int t) //返回最终的cost
    {
        int cost = 0;
        while(SPFA(s,t))
        {
            int cur = t,minflow = INF;
            while(cur != s)
            {
                if(minflow > Cap[pre_edge[cur]]-Flow[pre_edge[cur]])
                    minflow = Cap[pre_edge[cur]]-Flow[pre_edge[cur]];
                cur = Num[pre_edge[cur] ^ 1];
            }
            cur = t ;
            while(cur != s)
            {
                Flow[pre_edge[cur]] += minflow;
                Flow[pre_edge[cur] ^ 1] -= minflow;
                cost += minflow * Cost[pre_edge[cur]];
                cur = Num[pre_edge[cur] ^ 1];
            }
        }
        return cost;
    }
private:
    bool SPFA(int s,int t)
    {
        fill(Len,Len+M,INF);
        Len[s]=0;
        int head = -1,tail = -1,cur;
        Q[++head] = s;
        while(head != tail)
        {
            ++tail;
            if(tail >= M) tail = 0 ;
            cur = Q[tail];
            for(int i = Head[cur];i != -1;i = Next[i])
            {
                if(Cap[i]>Flow[i] && Len[Num[i]] > Len[cur] + Cost[i])
                {
                    Len[Num[i]] = Len[cur] + Cost[i];
                    pre_edge[Num[i]] = i;
                    if(!InQ[Num[i]])
                    {
                        InQ[Num[i]]=true;
                        ++head;
                        if(head >= M) head = 0;
                        Q[head] = Num[i];
                    }
                }
            }
            InQ[cur]=false;
        }
        return Len[t] != INF;
    }
    int top;
}my;