最大流Dinic

不断用BFS构造分层网络，用DFS增广。中途用取指的cur优化DFS。

Dinic封装模板：

 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #include <queue>
 using namespace std;
 typedef long long L;
 const int maxn =  + ;
 const int maxm =  + ;
 const int INF = -1u >> ;
 int fch[maxn], n, m;
 L ans = ;
 bool vis[maxn];
 struct Tedge{
     int from, to, cap, flow, next;
 }adj[maxm];
 struct Dinic{
     int S, T, n, ms;
     int d[maxn], cur[maxn], fch[maxn];
     void init(int n){
         this -> n = n;
         memset(fch, -, sizeof(fch));
         ms = ;
         return ;
     }
     void AddEdge(int u, int v, int c){
         adj[ms] = (Tedge){u, v, c, , fch[u]};
         fch[u] = ms ++;
         adj[ms] = (Tedge){v, u, , , fch[v]};
         fch[v] = ms ++;
         return ;
     }
     bool BFS(){
         memset(vis, , sizeof(vis));
         queue<int> Q;
         Q.push(S); vis[S] = true; d[S] = ;
         while(!Q.empty()){
             int x = Q.front(); Q.pop();
             for(int i = fch[x]; i != -; i = adj[i].next){
                 Tedge& e = adj[i];
                 if(!vis[e.to] && e.cap > e.flow){
                     vis[e.to] = true;
                     d[e.to] = d[x] + ;
                     Q.push(e.to);
                 }
             }
         }
         return vis[T];
     }
     int DFS(int x, int a){
         if(x == T || !a) return a;
         int flow = , f;
         for(int& i = cur[x]; i != -; i = adj[i].next){
             Tedge& e = adj[i];
             if(d[e.to] == d[x] +  && (f = DFS(e.to, min(a, e.cap - e.flow))) > ){
                 flow += f;
                 a -= f;
                 e.flow += f;
                 adj[i ^ ].flow -= f;
                 if(!a) break;
             }
         }
         return flow;
     }
     L Max_Flow(int S, int T){
         this -> S = S;
         this -> T = T;
         L flow = ;
         while(BFS()){
             for(int i = ; i < n; i ++) cur[i] = fch[i];
             flow += DFS(S, INF);
         }
         return flow;
     }
 }sol;
 void read(int &x){
     x = ; int sig = ; char ch = getchar();
     while(!isdigit(ch)) { if(ch == '-') sig = -; ch = getchar(); }
     while(isdigit(ch)) x =  * x + ch - '', ch = getchar();
     x *= sig; return ;
 }
 void init(){
     read(n); read(m);
     sol.init(n);
     int u, v, w;
     for(int i = ; i < m; i++){
         read(u); read(v); read(w);
         sol.AddEdge(u, v, w);
     }
     return ;
 }
 void work(){
     ans = sol.Max_Flow(, n);
     return ;
 }
 void print(){
     printf("%lld\n", ans);
     return ;
 }
 int main(){
     init();
     work();
     print();
     return ;
 }