COGS——C 14. [网络流24题] 搭配飞行员

 1 #include <algorithm>
 2 #include <cstring>
 3 #include <cstdio>
 4 
 5 using namespace std;
 6 
 7 const int INF(0x7fffffff);
 8 const int N(233);
 9 int n,n1,u,v,w;
10 
11 int head[N],sumedge;
12 struct Edge
13 {
14     int to,next,val;
15     Edge(int to=0,int next=0,int val=0):
16         to(to),next(next),val(val){}
17 }edge[N<<1];
18 inline void ins(int u,int v,int w)
19 {
20     edge[++sumedge]=Edge(v,head[u],w);
21     head[u]=sumedge;
22 }
23 struct Type_AC
24 {
25     int s,t,ret;
26     int deep[N];
27     bool BFS()
28     {
29         memset(deep,-1,sizeof(deep));
30         int tail=0,hd=0,que[N];
31         deep[s]=0; que[tail++]=s;
32         for(;hd<tail;)
33         {
34             int fro=que[hd++];
35             for(int i=head[fro];i;i=edge[i].next)
36             {
37                 int v=edge[i].to;
38                 if(deep[v]==-1&&edge[i].val)
39                 {
40                     deep[v]=deep[fro]+1;
41                     que[tail++]=v;
42                 }
43             }
44         }
45         if(deep[t]!=-1) return true;
46         return false;
47     }
48     int DFS(int now,int flow)
49     {
50         if(now==t||!flow) return flow;
51         int go,flux=0;
52         for(int i=head[now];i;i=edge[i].next)
53         {
54             int v=edge[i].to;
55             if(deep[v]!=deep[now]+1||edge[i].val<=0) continue;
56             go=DFS(v,min(edge[i].val,flow-flux));
57             edge[i].val-=go;
58             edge[i^1].val+=go;
59             flux+=go;
60             if(flux==flow) return flow;
61         }
62         if(!flux) deep[now]=-1;
63         return flux;
64     }
65     void Dinic()
66     {
67         for(;BFS();) ret+=DFS(s,INF);
68     }
69 }I_want_AC;
70 
71 int main()
72 {
73     freopen("flyer.in","r",stdin);
74     freopen("flyer.out","w",stdout);
75     
76     scanf("%d%d",&n,&n1);
77     for(int i=1;i<=n1;i++) ins(0,i,1),ins(i,0,0);
78     for(int i=n1+1;i<=n;i++) ins(i,n+1,1),ins(n+1,i,0);
79     for(;~scanf("%d%d",&u,&v);) ins(u,v,1); ins(v,u,0);
80     I_want_AC.s=0;
81     I_want_AC.t=n+1;
82     I_want_AC.Dinic();
83     printf("%d\n",I_want_AC.ret);
84     return 0;
85 }