模板：网络流最大流

Posted 2020-10-14

Edmonds-Karp算法：

 1 //Edmonds-Karp算法
 2 
 3 const int INF=0x3f3f3f3f;
 4 int n,m,s,t,Map[N][N],path[N],flow[N];
 5 
 6 int bfs(){
 7     int tmp;
 8     queue <int> Q;
 9     while(!Q.empty()) Q.pop();
10     memset(path,-1,sizeof(path));
11     path[s]=0;flow[s]=INF;
12     Q.push(s);
13     while(!Q.empty()){
14         tmp=Q.front();Q.pop();
15         if(tmp==t) break;
16         for(int i=1;i<=m;i++){
17             if(i!=s&&path[i]==-1&&Map[tmp][i]){
18                 flow[i]=flow[tmp]<Map[tmp][i]?flow[tmp]:Map[tmp][i];
19                 Q.push(i);
20                 path[i]=tmp;
21             }
22         }
23     }
24     if(path[t]==-1) return -1;
25     return flow[m];
26 }
27 
28 int Edmonds_Karp(){
29     int max_flow=0,step,now,pre;
30     while((step=bfs())!=-1){
31         max_flow+=step;
32         now=t;
33         while(now!=s){
34             pre=path[now];
35             Map[pre][now]-=step;
36             Map[now][pre]+=step;
37             now=pre;
38         }
39     }
40     return max_flow;
41 }