最小費用最大流

這裡只給出程式碼實現：

class flow_map
{
	private:
		int u;
		int s,t;
		int n,m;
		inline bool spfa()
		{
			memset(vis,0,sizeof(vis)),memset(dis,0x3f,sizeof(dis));
			queue<int> q;
			while(!q.empty()) q.pop();
			dis[s]=0,vis[s]=1,q.push(s),incf[s]=0x3f3f3f3f;
			register int u;
			while(!q.empty())
			{
				u=q.front(),q.pop(),vis[u]=0;
				for(register int j(head[u]);j;j=nex[j])
				{
					if(!flow[j]) continue;
					if(dis[to[j]]>dis[u]+cost[j])
					{
						dis[to[j]]=dis[u]+cost[j],
						incf[to[j]]=min(incf[u],flow[j]),
						pre[to[j]]=j;
						if(!vis[to[j]]) vis[to[j]]=1,q.push(to[j]);
					}
				}
			}
			return (dis[t]!=1061109567);
		}
		inline int against_edge(int id)
		{
			if(id&1) return (id+1);
			else return (id-1);
		}
	public:
		int edge_num;
		int to[maxm],head[maxn],nex[maxm],flow[maxm],cost[maxm];
		int dis[maxn];
		bool vis[maxn];
		int incf[maxn];
		int pre[maxn];
		int max_flow;
		inline void set()
		{
			read_(n),
			read_(m),
			read_(s),
			read_(t);
		}
		inline void add_edge(void)
		{
			++edge_num,
			read_(u),read_(to[edge_num]),
			read_(flow[edge_num]),
			read_(cost[edge_num]),
			nex[edge_num]=head[u],
			head[u]=edge_num;
		}
		inline void add_edge(int u,int v,int f,int c)
		{
			to[++edge_num]=v,
			nex[edge_num]=head[u],
			head[u]=edge_num,
			cost[edge_num]=c,
			flow[edge_num]=f;
		}
		inline void build()
		{
			for(register int i(0),u,v,w,c;i<m;++i)
				read_(u),
				read_(v),
				read_(w),
				read_(c),
				add_edge(u,v,w,c),
				add_edge(v,u,0,-c);
		}
		inline int max_flow__min_cost()
		{
			register int mxf(0),mic(0),x;
			while(spfa())
			{
				mxf+=incf[x=t],
				mic+=incf[t]*dis[t];
				while(x!=s)
					flow[pre[x]]-=incf[t],
					flow[against_edge(pre[x])]+=incf[t],
					x=to[against_edge(pre[x])];
			}
			return max_flow=mxf,mic;
		}
};