费用流板子 dij&spfa

struct edge{
    int to,cap,cost,rev;
};

int n,V,k;
int a[MAX_N];
vector<edge> G[2*MAX_N+2];
int h[2*MAX_N+2];
int dist[2*MAX_N+2];
int prevv[2*MAX_N+2],preve[2*MAX_N+2];

void add_edge(int from,int to,int cap,int cost){
    G[from].push_back((edge){to,cap,cost,G[to].size()});
    G[to].push_back((edge){from,0,-cost,G[from].size()-1});
}

int min_cost_flow(int s,int t,int f){
    int res=0;
    fill(h,h+V,0);
    while(f>0){
        priority_queue<P,vector<P>,greater<P> >que;
        fill(dist,dist+V,INF);
        dist[s]=0;
        que.push(P(0,s));
        while(!que.empty()){
            P p=que.top();que.pop();
            int v=p.second;
            if(dist[v]<p.first)continue;
            for(int i=0;i<G[v].size();i++){
                edge &e=G[v][i];
                if(e.cap>0&&dist[e.to]>dist[v]+e.cost+h[v]-h[e.to]){
                    dist[e.to]=dist[v]+e.cost+h[v]-h[e.to];
                    prevv[e.to]=v;
                    preve[e.to]=i;
                    que.push(P(dist[e.to],e.to));
                }
            }
        }
        if(dist[t]==INF)return -1;
        for(int v=0;v<V;v++)h[v]+=dist[v];
        int d=f;
        for(int v=t;v!=s;v=prevv[v]){
            d=min(d,G[prevv[v]][preve[v]].cap);
        }
        f-=d;
        res+=d*h[t];
        for(int v=t;v!=s;v=prevv[v]){
            edge &e=G[prevv[v]][preve[v]];
            e.cap-=d;
            G[v][e.rev].cap+=d;
        }
    }
    return res;
}

int head[maxn],Next[maxn*200],to[maxn*200];
int flow[maxn*200],dis[maxn],pre[maxn],vis[maxn],id[maxn],ct[maxn];
inline void add(int u,int v,int w,int cost){
    Next[cnt]=head[u];
    head[u]=cnt;
    to[cnt]=v;
    flow[cnt]=w;
    ct[cnt++]=cost;

    Next[cnt]=head[v];
    head[v]=cnt;
    to[cnt]=u;
    flow[cnt]=0;
    ct[cnt++]=-cost;
}
bool spfa(){
    memset(vis,0,sizeof(vis));
    memset(dis,inf,sizeof(dis));
    memset(pre,-1,sizeof(pre));
    dis[s]=0;
    queue<int> q;
    q.push(s);
    while(!q.empty()){
        int u=q.front();
        q.pop();
        vis[u]=0;
        for(int i=head[u];i!=-1;i=Next[i]){
            int v=to[i];
            int d=ct[i];
            if(dis[v]>dis[u]+d&&flow[i]>0){
                dis[v]=dis[u]+d;
                pre[v]=u;
                id[v]=i;
                if(!vis[v]){
                    vis[v]=1;
                    q.push(v);
                }
            }
        }
    }
   // cout<<dis[t]<<endl;
    return dis[t]<inf;
}
int Maxflow(){
    int ans=0;
    while(spfa()){ 
        int Min=inf;
        for(int i=t;i!=s;i=pre[i]){
        //    cout<<i<<" "<<pre[i]<<endl;
            Min=min(flow[id[i]],Min);
        }
        for(int i=t;i!=s;i=pre[i]){
            flow[id[i]]-=Min;
            flow[id[i]^1]+=Min;
        }
        ans+=dis[t]*Min;
       
    }
    return ans;
}