Dinic

 1 #include<iostream>
 2 #include<vector>
 3 #include<queue>
 4 #include<cstring>
 5 using namespace std;
 6 const int maxn=1024;
 7 const int inf=1<<30;
 8 struct Edge{
 9     int from,to,flow,cap;
10 };
11 struct Dinic{
12     int vis[maxn],cur[maxn],d[maxn];
13     vector<Edge> edges;
14     vector<int> G[maxn];
15     int s,t;
16     void addEdge(int from,int to,int cap)
17     {
18         edges.push_back((Edge){from,to,0,cap});
19         G[from].push_back(edges.size()-1);
20         edges.push_back((Edge){to,from,0,0});
21         G[to].push_back(edges.size()-1);
22     }
23     int BFS()
24     {
25         memset(vis,0,sizeof(vis));
26         queue<int> Q;
27         Q.push(s);
28         vis[s]=1;
29         d[s]=0;
30         while(!Q.empty()){
31             int x=Q.front();Q.pop();
32             for(int i=0;i<G[x].size();i++){
33                 Edge& e=edges[G[x][i]];
34                 if(!vis[e.to]&&e.cap>e.flow){
35                     vis[e.to]=1;
36                     d[e.to]=d[x]+1;
37                     Q.push(e.to);
38                 }
39             }
40         }
41         return vis[t];
42     }
43     int DFS(int u,int a)
44     {
45         if(u==t||a==0) return a;
46         int flow=0,f;
47         for(int& i=cur[u];i<G[u].size();i++){
48             Edge& e=edges[G[u][i]];
49             if(d[e.to]==d[u]+1&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0){
50                 e.flow+=f;
51                 edges[G[u][i]^1].flow-=f;
52                 flow+=f;
53                 a-=f;
54                 if(!a) break;
55             }
56         }
57         return flow;
58     }
59     int MaxFlow(int ss,int tt)
60     {
61         int ans=0;
62         s=ss,t=tt;
63         while(BFS()){
64             memset(cur,0,sizeof(cur));
65             ans+=DFS(s,inf);
66         }
67         return ans;
68     }
69 };
70 Dinic solver;
71 int main()
72 {
73     int n,m;
74     cin>>n>>m;
75     for(int i=1;i<=m;i++){
76         int from,to,cap;
77         cin>>from>>to>>cap;
78         solver.addEdge(from,to,cap);
79     }
80     cout<<solver.MaxFlow(1,n);
81     return 0;
82 }