zkw费用流

inline bool SPFA()
{
    memset(dis,0x3f,sizeof(dis));
    dis[T]=0;q.push(T);
    while(!q.empty())
    {
        int tmp=q.front();q.pop();
        b[tmp]=0;
        for(int i=head[tmp];i;i=a[i].nxt)
          if(dis[a[i].to]>dis[tmp]+a[i^1].cost&&a[i^1].remain)
          {
            dis[a[i].to]=dis[tmp]+a[i^1].cost;
            if(!b[a[i].to]) b[a[i].to]=1,q.push(a[i].to);
          }
    }
    return dis[S]int dfs(int now,int limit,int cost)
{
    vis[now]=1;
    if(now==T||!limit) return ans2+=limit*cost,limit;
    int flow=0,f;
    for(int i=head[now];i;i=a[i].nxt)
      if(dis[now]-a[i].cost==dis[a[i].to]&&a[i].remain&&!vis[a[i].to]&&(f=dfs(a[i].to,min(limit,a[i].remain),cost+a[i].cost)))
      {
        limit-=f,flow+=f,a[i].remain-=f,a[i^1].remain+=f;
        if(!limit) return flow;
      }
    dis[now]=-1;return flow;
}
inline void zkw()
{
    while(SPFA())
      do
      {
        memset(vis,0,sizeof(vis));
        ans1+=dfs(S,INF,0);
      }
      while(vis[T]);
}