MCMF.cpp

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <vector>
using namespace std;
const int maxn=2007;
const int INF=0x7fffffff;
struct Edge{
	int from,to,cap,flow,cost;
};
struct MCMF{
	int n,m,s,t;
	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) {   //cost 是每流过一个单位所需费用
		 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,int& 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[u],e.cap-e.flow);
						 if(!inq[e.to]){ Q.push(e.to); inq[e.to]=1; }
					}
			  }
		 }
		 if(d[t]==INF)  return false;  //s-t 不连通，失败退出
		 flow+=a[t];
		 cost+=d[t]*a[t];
		 int u=t;
		 while(u!=s){
			 edges[p[u]].flow+=a[t];
			 edges[p[u]^1].flow-=a[t];
			 u=edges[p[u]].from;
		 }
		 return true;
	}
 
	int Mincost(int s,int t){  //求最大流的最小费用
		int flow=0,cost=0;
		while(BellmanFord(s,t,flow,cost));
		return cost;
	}
}mcmf;