网络流最大流模板（洛谷3376）——Dinic

 1 #include<queue>
 2 #include<vector>
 3 #include<iostream>
 4 #include<algorithm>
 5 #include<cstring>
 6 #include<cstdlib>
 7 #include<cstdio>
 8 using namespace std;
 9 const int N=100111,iNF=0x7fffffff;
10 struct edge{int from,to,cap,flow;};
11 int n,m,sx,tx,res,crt[N],depth[N];
12 vector<int> gr[N];
13 vector<edge> e;
14 
15 bool bfs(){
16     bool vis[N];memset(vis,0,sizeof vis);
17     memset(depth,0,sizeof depth);
18     queue<int> q;q.push(sx);vis[sx]=true;
19     
20     while(!q.empty()){
21         int x=q.front();q.pop();
22         for(int i=0;i<gr[x].size();i++){
23             edge &u=e[gr[x][i]];
24             if(!vis[u.to]&&u.cap>u.flow){
25                 vis[u.to]=true;
26                 depth[u.to]=depth[x]+1;
27                 q.push(u.to);
28             }
29         }
30     }
31     return vis[tx];
32 }
33 
34 int dfs(int x,int v){
35     if(x==tx||v==0)return v;
36     int flow=0,f;
37     for(int &i=crt[x];i<gr[x].size();i++){
38         edge &u=e[gr[x][i]];
39         if(depth[u.to]==depth[x]+1&&(f=dfs(u.to,min(v,u.cap-u.flow)))>0){
40             u.flow+=f;
41             e[gr[x][i]^1].flow-=f;
42             flow+=f;
43             v-=f;
44             
45             if(v==0)break;
46         }
47     }
48     return flow;
49 }
50 
51 int main(){
52     ios::sync_with_stdio(false);
53     freopen("Dinic.in","r",stdin);
54     cin>>n>>m>>sx>>tx;
55     while(m--){
56         int x,y,v;cin>>x>>y>>v;
57         e.push_back((edge){x,y,v,0});
58         e.push_back((edge){y,x,0,0});
59         gr[x].push_back(e.size()-2);
60         gr[y].push_back(e.size()-1);
61     }
62     while(bfs()){
63         memset(crt,0,sizeof crt);
64         res+=dfs(sx,iNF);
65     }
66     cout<<res<<endl;
67     return 0;
68 }