【网络流】【Dinic】Dinic模板

注意：有时加边不一定要加反向弧。

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<queue>
 5 using namespace std;
 6 #define INF 2147483647
 7 #define MAXN 20011
 8 #define MAXM 600301
 9 int v[MAXM],cap[MAXM],en,first[MAXN],next[MAXM];
10 int d[MAXN],cur[MAXN],S,T;
11 queue<int>q;
12 int n,m;
13 void Init_Dinic(){memset(first,-1,sizeof(first)); en=0;}
14 void AddEdge(const int &U,const int &V,const int &W)
15 {
16     v[en]=V; cap[en]=W;
17     next[en]=first[U];
18     first[U]=en++;
19     v[en]=V;
20     next[en]=first[U];
21     first[U]=en++;
22 }
23 bool bfs()
24 {
25     memset(d,-1,sizeof(d)); q.push(S); d[S]=0;
26     while(!q.empty())
27       {
28           int U=q.front(); q.pop();
29           for(int i=first[U];i!=-1;i=next[i])
30             if(d[v[i]]==-1 && cap[i])
31               {
32                 d[v[i]]=d[U]+1;
33                 q.push(v[i]);
34               }
35       }
36     return d[T]!=-1;
37 }
38 int dfs(int U,int a)
39 {
40     if(U==T || !a) return a;
41     int Flow=0,f;
42     for(int &i=cur[U];i!=-1;i=next[i])
43       if(d[U]+1==d[v[i]] && (f=dfs(v[i],min(a,cap[i]))))
44         {
45           cap[i]-=f; cap[i^1]+=f;
46           Flow+=f; a-=f; if(!a) break;
47         }
48     if(!Flow) d[U]=-1;
49     return Flow;
50 }
51 int max_flow()
52 {
53     int Flow=0,tmp=0;
54     while(bfs())
55       {
56           memcpy(cur,first,(n+5)*sizeof(int));
57           while(tmp=dfs(S,INF)) Flow+=tmp;
58       }
59     return Flow;
60 }