洛谷P1894 [USACO4.2]完美的牛栏The Perfect Stall

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 1 #include<cstdio>
 2 #include<cstring>
 3 #include<cmath>
 4 #include<algorithm>
 5 #include<queue>
 6 using namespace std;
 7 const int MAXN=2*1e6+10;
 8 const int INF=0x7fffff;
 9 inline int read()
10 {
11     char c=getchar();int flag=1,x=0;
12     while(c<'0'||c>'9')    {if(c=='-')    flag=-1;c=getchar();}
13     while(c>='0'&&c<='9')    x=x*10+c-48,c=getchar();return x*flag;
14 }
15 struct node
16 {
17     int u,v,f,nxt;
18 }edge[MAXN];
19 int head[MAXN],cur[MAXN];
20 int num=0;
21 inline void add_edge(int x,int y,int z)
22 {
23     edge[num].u=x;
24     edge[num].v=y;
25     edge[num].f=z;
26     edge[num].nxt=head[x];
27     head[x]=num++;
28 }
29 inline void add(int x,int y,int z)
30 {
31     add_edge(x,y,z);
32     add_edge(y,x,0);
33 }
34 int n,m,e;
35 int S=0,T=MAXN-1;
36 int deep[MAXN];
37 inline bool BFS()
38 {
39     memset(deep,0,sizeof(deep));
40     queue<int>q;q.push(S);deep[S]=1;
41     while(q.size()!=0)
42     {
43         int p=q.front();q.pop();
44         for(int i=head[p];i!=-1;i=edge[i].nxt)
45             if(edge[i].f&&deep[edge[i].v]==0)
46                 deep[edge[i].v]=deep[p]+1,q.push(edge[i].v);
47     }
48     return deep[T];
49 }
50 int dfs(int now,int nowflow)
51 {
52     if(now==T||nowflow<=0)    return nowflow;
53     int totflow=0;
54     for(int &i=cur[now];i!=-1;i=edge[i].nxt)
55     {
56         if(edge[i].f&&deep[edge[i].v]==deep[edge[i].u]+1)
57         {
58             int canflow=dfs(edge[i].v,min(edge[i].f,nowflow));
59             totflow+=canflow;
60             nowflow-=canflow;
61             edge[i].f-=canflow;
62             edge[i^1].f+=canflow;
63             if(nowflow<=0)    break;
64         }
65     }
66     return totflow;
67 }
68 inline void Dinic()
69 {
70     int ans=0;
71     while(BFS())
72     {
73         memcpy(cur,head,sizeof(head));
74         ans+=dfs(S,INF);
75     }
76     printf("%d",ans);
77 }
78 int main()
79 {
80     memset(head,-1,sizeof(head));
81     n=read();m=read();
82     for(int i=1;i<=n;i++)    add(S,i,1);
83     for(int i=1;i<=m;i++)    add(i+n,T,1);
84     for(int i=1;i<=n;i++)
85     {
86         int num=read();
87         for(int j=1;j<=num;j++)
88         {
89             int how=read();
90             add(i,how+n,1);
91         }
92     }
93     Dinic();
94     return 0;
95 }