【模板】最小费用路算法

摘自刘汝佳《算法竞赛入门经典（第2版）》

#include<cstdio>
#include<queue>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;
const int maxn=1e5+10;
const int INF=0x3f3f3f3f;
struct Edge{
    int from,to,cap,flow,cost;
    Edge(int u,int v,int c,int f,int w):from(u),to(v),cap(c),flow(f),cost(w){}
};
struct MCMF{
    int n,m;
    vector<Edge>edges;
    vector<int>G[maxn];
    int inq[maxn];//是否在队列中
    int d[maxn];//Bellman-Ford
    int p[maxn];//上一条弧
    int a[maxn];//可改进量 
    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 cap,int cost)
    {
        edges.push_back(Edge(from,to,cap,0,cost));
        edges.push_back(Edge(to,from,0,0,-cost));
        m=edges.size();
        G[from].push_back(m-2);
        G[to].push_back(m-1);
    }
    bool BellmanFord(int s,int t,int &flow,long long &cost)
    {
        for(int i=0;i<n;i++)d[i]=INF;
        memset(inq,0,sizeof(inq));
        d[s]=0;inq[s]=1;p[s]=0;a[s]=INF;
        queue<int>Q;
        Q.push(s);
        while(!Q.empty())
        {
            int u=Q.front();Q.pop();
            inq[u]=0;
            for(int i=0;i<G[u].size();i++)
            {
                Edge &e=edges[G[u][i]];
                if(e.cap>e.flow&&d[e.to]>d[u]+e.cost)
                {
                    d[e.to]=d[u]+e.cost;
                    p[e.to]=G[u][i];
                    a[e.to]=min(a[e.to],e.cap-e.flow);
                    if(!inq[e.to])
                    {
                        Q.push(e.to);
                        inq[e.to]=1;
                    }
                }
            }
        }
        if(d[t]==INF)return false;
        flow+=a[t];
        cost+=(long long)d[t]*(long long)a[t];
        for(int u=t;u!=s;u=edges[p[u]].from)
        {
            edges[p[u]].flow+=a[t];
            edges[p[u]^1].flow+=-a[t];
        }
        return true;
    }
    //需要保证初始网络中没有负权圈 
    int MincostMaxflow(int s,int t,long long&cost)
    {
        int flow=0;cost=0;
        while(BellmanFord(s,t,flow,cost));
        return flow;
    }
};
int main()
{
    return 0;
}