P3376 【模板】网络最大流（当前弧优化版dinic做法）

https://www.luogu.org/problem/P3376

模板题，dinic做法

 1 #define bug(x) cout<<#x<<" is "<<x<<endl
 2 #define IO std::ios::sync_with_stdio(0)
 3 #include <bits/stdc++.h>
 4 #define iter ::iterator
 5 #define pa pair<int,int>
 6 using namespace  std;
 7 #define ll long long
 8 #define mk make_pair
 9 #define pb push_back
10 #define se second
11 #define fi first
12 #define ls o<<1
13 #define rs o<<1|1
14 ll mod=998244353;
15 const int inf=2e9+10;
16 const int N=1e5+5,M=4e5+5;
17 struct node{
18     int cnt;
19     int head[N];
20     int nex[M];
21     int W[M];
22     int V[M];
23     int dep[N];
24     int cur[N];
25     int n,s,t;
26     void init(){
27         cnt=-1;
28         memset(head,-1,sizeof(head));
29         memset(nex,-1,sizeof(nex));
30     }
31     void _add(int u,int v,int w){
32         cnt++;
33         nex[cnt]=head[u];
34         head[u]=cnt;
35         V[cnt]=v;
36         W[cnt]=w;
37     }
38     void add(int u,int v,int w){
39         _add(u,v,w);
40         _add(v,u,0);
41     }
42     int dfs(int u,int flow){
43         if(u==t)return flow;
44         for(int i=cur[u];i!=-1;i=nex[i]){
45             if((dep[V[i]])==dep[u]+1&&W[i]){
46                 int di=dfs(V[i],min(flow,W[i]));
47                 if(di>0){
48                     W[i]-=di;
49                     W[i^1]+=di;
50                     return di;
51                 }
52             }
53         }
54         return 0;
55     }
56     int bfs(){
57         queue<int>q;
58         memset(dep,0,sizeof(dep));
59         dep[s]=1;
60         q.push(s);
61         while(!q.empty()){
62             int u=q.front();
63             q.pop();
64             for(int i=head[u];i!=-1;i=nex[i]){
65                 if(!dep[V[i]]&&W[i]>0){
66                     dep[V[i]]=dep[u]+1;
67                     q.push(V[i]);
68                 }
69             }
70         }
71         if(dep[t]>0)return 1;
72         return 0;
73     }
74     int dinic(){
75         int res=0;
76         while(bfs()){
77             for(int i=1;i<=n;i++)cur[i]=head[i];
78             while(int d=dfs(s,inf))res+=d;
79         }
80         return res;
81     }
82 };
83 int main(){
84     int n,m,s,t;
85     scanf("%d%d%d%d",&n,&m,&s,&t);
86     node ac;
87     ac.init();
88     ac.n=n;
89     ac.s=s;
90     ac.t=t;
91     for(int i=1;i<=m;i++){
92         int x,y,z;
93         scanf("%d%d%d",&x,&y,&z);
94         ac.add(x,y,z);
95     }
96     printf("%d\n",ac.dinic());
97 }