注意：有时加边不一定要加反向弧。
Next Array版。
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]; 11 queue<int>q; 12 int n,m,S,T; 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]; first[U]=en++; 18 v[en]=U; cap[en]=0; 19 next[en]=first[V]; first[V]=en++; 20 } 21 bool bfs() 22 { 23 memset(d,-1,sizeof(d)); q.push(S); d[S]=0; 24 while(!q.empty()) 25 { 26 int U=q.front(); q.pop(); 27 for(int i=first[U];i!=-1;i=next[i]) 28 if(d[v[i]]==-1 && cap[i]) 29 { 30 d[v[i]]=d[U]+1; 31 q.push(v[i]); 32 } 33 } 34 return d[T]!=-1; 35 } 36 int dfs(int U,int a) 37 { 38 if(U==T || !a) return a; 39 int Flow=0,f; 40 for(int &i=cur[U];i!=-1;i=next[i]) 41 if(d[U]+1==d[v[i]] && (f=dfs(v[i],min(a,cap[i])))) 42 { 43 cap[i]-=f; cap[i^1]+=f; 44 Flow+=f; a-=f; if(!a) break; 45 } 46 if(!Flow) d[U]=-1; 47 return Flow; 48 } 49 int max_flow() 50 { 51 int Flow=0,tmp=0; 52 while(bfs()) 53 { 54 memcpy(cur,first,(n+5)*sizeof(int)); 55 while(tmp=dfs(S,INF)) Flow+=tmp; 56 } 57 return Flow; 58 }