BZOJ 1497: [NOI2006]最大获利（最大权闭合图）

http://www.lydsy.com/JudgeOnline/problem.php?id=1497

题意：

思路：

论文题，只要看过论文的话就是小菜一碟啦~

每个用户群i作为一个结点分别向相应的中转站ai和中转站bi连有向边。

 #include<iostream>
 #include<algorithm>
 #include<cstring>
 #include<cstdio>
 #include<vector>
 #include<stack>
 #include<queue>
 #include<cmath>
 #include<map>
 #include<set>
 using namespace std;
 typedef long long ll;
 typedef pair<int,int> pll;
 const int INF = 0x3f3f3f3f;
 const int maxn =  + ;

 int n, m;
 int val[maxn];

 struct Edge
 {
     int from,to,cap,flow;
     Edge(int u,int v,int w,int f):from(u),to(v),cap(w),flow(f){}
 };

 struct Dinic
 {
     int n,m,s,t;
     vector<Edge> edges;
     vector<int> G[maxn];
     bool vis[maxn];
     int cur[maxn];
     int d[maxn];

     void init(int n)
     {
         this->n=n;
         for(int i=;i<n;++i) G[i].clear();
         edges.clear();
     }

     void AddEdge(int from,int to,int cap)
     {
         edges.push_back( Edge(from,to,cap,) );
         edges.push_back( Edge(to,from,,) );
         m=edges.size();
         G[from].push_back(m-);
         G[to].push_back(m-);
     }

     bool BFS()
     {
         queue<int> Q;
         memset(vis,,sizeof(vis));
         vis[s]=true;
         d[s]=;
         Q.push(s);
         while(!Q.empty())
         {
             int x=Q.front(); Q.pop();
             for(int i=;i<G[x].size();++i)
             {
                 Edge& e=edges[G[x][i]];
                 if(!vis[e.to] && e.cap>e.flow)
                 {
                     vis[e.to]=true;
                     d[e.to]=d[x]+;
                     Q.push(e.to);
                 }
             }
         }
         return vis[t];
     }

     int DFS(int x,int a)
     {
         if(x==t || a==) return a;
         int flow=, f;
         for(int &i=cur[x];i<G[x].size();++i)
         {
             Edge &e=edges[G[x][i]];
             if(d[e.to]==d[x]+ && (f=DFS(e.to,min(a,e.cap-e.flow) ) )>)
             {
                 e.flow +=f;
                 edges[G[x][i]^].flow -=f;
                 flow +=f;
                 a -=f;
                 if(a==) break;
             }
         }
         return flow;
     }

     int Maxflow(int s,int t)
     {
         this->s=s; this->t=t;
         int flow=;
         while(BFS())
         {
             memset(cur,,sizeof(cur));
             flow +=DFS(s,INF);
         }
         return flow;
     }
 }DC;

 int main()
 {
     //freopen("in.txt","r",stdin);
     while(~scanf("%d%d",&n,&m))
     {
         int src = , dst = n+m+;
         DC.init(dst+);
         for(int i=;i<=n;i++)
         {
             scanf("%d",&val[i]);
             DC.AddEdge(i,dst,val[i]);
         }
         int sum = ;
         for(int i=;i<=m;i++)
         {
             int a,b,c;
             scanf("%d%d%d",&a,&b,&c);
             DC.AddEdge(src,i+n,c);
             DC.AddEdge(i+n,a,INF);
             DC.AddEdge(i+n,b,INF);
             sum+=c;
         }
         int ans = sum-DC.Maxflow(src,dst);
         printf("%d\n",ans);
     }
     return ;
 }