最小费用流

const int MAXN = 200010;const int MAXM = 1200010;const int INF = 0x3f3f3f3f;struct Edge {    int to,next,cap,flow,cost;} edge[MAXM];int head[MAXN],tol;int pre[MAXN],dis[MAXN];bool vis[MAXN];int N;//节点总个数，节点编号从0~N-1void init(int n){    N = n;    tol = 0;    memset(head,-1,sizeof(head));}void addedge(int u,int v,int cap,int cost){    edge[tol].to = v;    edge[tol].cap = cap;    edge[tol].cost = cost;    edge[tol].flow = 0;    edge[tol].next = head[u];    head[u] = tol++;    edge[tol].to = u;    edge[tol].cap = 0;    edge[tol].cost = -cost;    edge[tol].flow = 0;    edge[tol].next = head[v];    head[v] = tol++;}bool spfa(int s,int t){    queue<int>q;    for(int i = 0; i < N; i++) {        dis[i] = INF;        vis[i] = false;        pre[i] = -1;    }    dis[s] = 0;    vis[s] = true;    q.push(s);    while(!q.empty()) {        int u = q.front();        q.pop();        vis[u] = false;        for(int i = head[u]; i != -1; i = edge[i].next) {            int v = edge[i].to;            if(edge[i].cap > edge[i].flow &&                    dis[v] > dis[u] + edge[i].cost ) {                dis[v] = dis[u] + edge[i].cost;                pre[v] = i;                if(!vis[v]) {                    vis[v] = true;                    q.push(v);                }            }        }    }    if(pre[t] == -1)return false;    else return true;}//返回的是最大流，cost存的是最小费用int minCostMaxflow(int s,int t,int &cost,int n){    int flow = 0;    cost = 0;    while(spfa(s,t)) {         if(flow>1) break;        int Min = INF;        for(int i = pre[t]; i != -1; i = pre[edge[i^1].to]) {            if(Min > edge[i].cap - edge[i].flow)                Min = edge[i].cap - edge[i].flow;        }        for(int i = pre[t]; i != -1; i = pre[edge[i^1].to]) {            edge[i].flow += Min;            edge[i^1].flow -= Min;            cost += edge[i].cost * Min;        }        flow += Min;//        cout<<flow<<endl;    }    return flow;}