【网络流】【Dinic】【最大流】bzoj3396 [Usaco2009 Jan]Total flow 水流

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<queue>
 using namespace std;
 #define INF 2147483647
 #define MAXN 201
 #define MAXM 1501
 int v[MAXM],cap[MAXM],en,first[MAXN],next[MAXM];
 int d[MAXN],cur[MAXN];
 queue<int>q;
 int m,S,T,W;
 char U[],V[];
 void Init_Dinic(){memset(first,-,sizeof(first)); en=; S='A'; T='Z';}
 void AddEdge(const int &U,const int &V,const int &W)
 {v[en]=V; cap[en]=W; next[en]=first[U]; first[U]=en++;
 v[en]=U; next[en]=first[V]; first[V]=en++;}
 bool bfs()
 {
     memset(d,-,sizeof(d)); q.push(S); d[S]=;
     while(!q.empty())
       {
         int U=q.front(); q.pop();
         for(int i=first[U];i!=-;i=next[i])
           if(d[v[i]]==- && cap[i])
             {
               d[v[i]]=d[U]+;
               q.push(v[i]);
             }
       }
     return d[T]!=-;
 }
 int dfs(int U,int a)
 {
     if(U==T || !a) return a;
     int Flow=,f;
     for(int &i=cur[U];i!=-;i=next[i])
       if(d[U]+==d[v[i]] && (f=dfs(v[i],min(a,cap[i]))))
         {
           cap[i]-=f; cap[i^]+=f;
           Flow+=f; a-=f; if(!a) break;
         }
     if(!Flow) d[U]=-;
     return Flow;
 }
 int max_flow()
 {
     int Flow=,tmp=;
     while(bfs())
       {
         memcpy(cur,first,sizeof(cur));
         while(tmp=dfs(S,INF)) Flow+=tmp;
       }
     return Flow;
 }
 int main()
 {
     scanf("%d",&m); Init_Dinic();
     for(int i=;i<=m;++i)
       {
           scanf("%s%s%d",U,V,&W);
           AddEdge(U[],V[],W);
       }
     printf("%d\n",max_flow());
     return ;
 }