费用流

const int inf = 0x3f3f3f3f;
struct mcmf{
    int he[maxn],tot,edge[maxm],ne[maxm],ver[maxm],cost[maxm];
    int pre[maxn],d[maxn];
    bool vis[maxn];
    int n;
    void init(int x){
        n = x;
        tot = 1;
        for( int i = 0;i <= n;i++ ) he[i] = 0;
    }
    void add(int x,int y,int cap,int c){
        ver[++tot] = y;
        ne[tot] = he[x];
        he[x] = tot;
        edge[tot] = cap;
        cost[tot] = c;
        ver[++tot] = x;
        ne[tot] = he[y];
        he[y] = tot;
        edge[tot] = 0;
        cost[tot] = -c;
    }
    bool spfa(int s,int t){
        queue<int>q;
        for(int i = 0;i < n;i++){
            d[i] = inf;
            vis[i] = false;
            pre[i] = -1;
        }
        d[s] = 0;
        vis[s] = true;
        q.push(s);
        while(!q.empty()){
            int x = q.front();
            q.pop();
            vis[x] = false;
            for(int cure = he[x]; cure ;cure = ne[cure]){
                int y = ver[cure];
                if(edge[cure] && d[y] > d[x] + cost[cure] ){
                    d[y] = d[x] + cost[cure];
                    pre[y] = cure;
                    if(!vis[y]){
                        vis[y] = true;
                        q.push(y);
                    }
                }
            }
        }
        if(pre[t] == -1)return false;
        else return true;
    }

    int mincost(int s,int t,int &cc){
        int flow = 0;
        cc = 0;
        while(spfa(s,t)){
            int mn = inf;
            for(int cure = pre[t];cure != -1;cure = pre[ ver[cure^1] ]){
                if(mn > edge[cure])
                    mn = edge[cure];
            }
            for(int cure = pre[t];cure != -1;cure = pre[ ver[cure^1] ]){
                edge[cure] -= mn;
                edge[cure^1] += mn;
                cc += cost[cure] * mn;
            }
            flow += mn;
        }
        return flow;
    }
} g;