【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[1],V[1];
void Init_Dinic(){memset(first,-1,sizeof(first)); en=0; 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,-1,sizeof(d)); q.push(S); d[S]=0;
    while(!q.empty())
      {
        int U=q.front(); q.pop();
        for(int i=first[U];i!=-1;i=next[i])
          if(d[v[i]]==-1 && cap[i])
            {
              d[v[i]]=d[U]+1;
              q.push(v[i]);
            }
      }
    return d[T]!=-1;
}
int dfs(int U,int a)
{
    if(U==T || !a) return a;
    int Flow=0,f;
    for(int &i=cur[U];i!=-1;i=next[i])
      if(d[U]+1==d[v[i]] && (f=dfs(v[i],min(a,cap[i]))))
        {
          cap[i]-=f; cap[i^1]+=f;
          Flow+=f; a-=f; if(!a) break;
        }
    if(!Flow) d[U]=-1;
    return Flow;
}
int max_flow()
{
    int Flow=0,tmp=0;
    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=1;i<=m;++i)
      {
          scanf("%s%s%d",U,V,&W);
          AddEdge(U[0],V[0],W);
      }
    printf("%d\n",max_flow());
    return 0;
}