BZOJ2502: 清理雪道

有下界的最小流

注意推流操作
切边然后重连边

#include<cstdio>
#include<cmath>
#include<queue>
#include<iostream>
#include<cstring>
using namespace std;



struct Chain
{
   int u,flow;
   Chain *next,*Pair;
}*Head[10001];

inline void Add(int u,int v,int flow)
{  
 Chain *tp=new Chain;
 tp->next=Head[u];tp->u=v;tp->flow=flow;Head[u]=tp;
 tp=new Chain;
 tp->next=Head[v];tp->u=u;tp->flow=0;Head[v]=tp;
 Head[u]->Pair=Head[v];Head[v]->Pair=Head[u];
}
int S,T;
const
  int INF=1<<29;
int H[1000001];
queue<int>Q;
inline bool BFS()
{
    memset(H,-1,sizeof(H));
    H[S]=1;
    Q.push(S);
    while(!Q.empty())
     {
        int u=Q.front();
         Q.pop();
        for(Chain *tp=Head[u];tp;tp=tp->next)
         if(H[tp->u]==-1&&tp->flow)
           H[tp->u]=H[u]+1,Q.push(tp->u);
     }
   return H[T]!=-1;
}

int DFS(int u,int flow)
{
    int res=flow,t;
    if(u==T)return flow;
    for(Chain *tp=Head[u];tp;tp=tp->next)
    if(H[tp->u]==H[u]+1&&tp->flow)
    { 
         t=DFS(tp->u,min(res,tp->flow)) ;
         res-=t;
         tp->flow-=t;
         tp->Pair->flow+=t;
         if(!res)return flow; 
    }
    if(res)H[u]=-1;
    return flow-res;
}

inline int Dinic()
{
    int res=0,t;
   while(BFS())res+=t=DFS(S,INF);
   return res; 
}
int In[101];

char c;
inline void read(int &a)
{
 a=0;do c=getchar();while(c<'0'||c>'9');
 while(c<='9'&&c>='0')a=(a<<3)+(a<<1)+c-'0',c=getchar();
}
bool R[1001];
int main()
{

    int n,i,s,e,j,k,l,t;
    read(n);
    S=n+1;
    T=n+2;
    s=n+3,e=n+4;
    for(i=1;i<=n;i++)
     {
       read(t);
       In[i]+=t;
       while(t--)
        {
          read(j);
          In[j]--;
          Add(i,j,INF);
        }
     }
    Add(e,s,INF);
    for(i=1;i<=n;Add(s,i++,INF),Add(i-1,e,INF))
     if(In[i]<0)
         Add(S,i,-In[i]);
      else Add(i,T,In[i]);
// Add(S,s,INF);
// Add(e,T,INF);
   Dinic();
   long long f1=0;
   for(Chain *tp=Head[S];tp;tp=tp->next)
     tp->flow=tp->Pair->flow=0;
   for(Chain *tp=Head[T];tp;tp=tp->next)
     tp->flow=tp->Pair->flow=0;
   for(Chain *tp=Head[e];tp;tp=tp->next)
      if(tp->u==s)
         f1+=tp->Pair->flow,tp->flow=tp->Pair->flow=0;
   Add(S,e,INF);
   Add(s,T,INF);
   long long f2=Dinic();
   printf("%lld\n",f1-f2);
   return 0;
}