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：
1 #include <cstdio> 2 #include <iostream> 3 #include <algorithm> 4 #include <cstring> 5 #include <cmath> 6 #include <queue> 7 using namespace std; 8 typedef long long L; 9 const int maxn = 10000 + 10; 10 const int maxm = 80000 + 10; 11 const int INF = -1u >> 1; 12 int fch[maxn], n, m; 13 L ans = 0; 14 bool vis[maxn]; 15 struct Tedge{ 16 int from, to, cap, flow, next; 17 }adj[maxm]; 18 struct Dinic{ 19 int S, T, n, ms; 20 int d[maxn], cur[maxn], fch[maxn]; 21 void init(int n){ 22 this -> n = n; 23 memset(fch, -1, sizeof(fch)); 24 ms = 0; 25 return ; 26 } 27 void AddEdge(int u, int v, int c){ 28 adj[ms] = (Tedge){u, v, c, 0, fch[u]}; 29 fch[u] = ms ++; 30 adj[ms] = (Tedge){v, u, 0, 0, fch[v]}; 31 fch[v] = ms ++; 32 return ; 33 } 34 bool BFS(){ 35 memset(vis, 0, sizeof(vis)); 36 queue<int> Q; 37 Q.push(S); vis[S] = true; d[S] = 0; 38 while(!Q.empty()){ 39 int x = Q.front(); Q.pop(); 40 for(int i = fch[x]; i != -1; i = adj[i].next){ 41 Tedge& e = adj[i]; 42 if(!vis[e.to] && e.cap > e.flow){ 43 vis[e.to] = true; 44 d[e.to] = d[x] + 1; 45 Q.push(e.to); 46 } 47 } 48 } 49 return vis[T]; 50 } 51 int DFS(int x, int a){ 52 if(x == T || !a) return a; 53 int flow = 0, f; 54 for(int& i = cur[x]; i != -1; i = adj[i].next){ 55 Tedge& e = adj[i]; 56 if(d[e.to] == d[x] + 1 && (f = DFS(e.to, min(a, e.cap - e.flow))) > 0){ 57 flow += f; 58 a -= f; 59 e.flow += f; 60 adj[i ^ 1].flow -= f; 61 if(!a) break; 62 } 63 } 64 return flow; 65 } 66 L Max_Flow(int S, int T){ 67 this -> S = S; 68 this -> T = T; 69 L flow = 0; 70 while(BFS()){ 71 for(int i = 0; i < n; i ++) cur[i] = fch[i]; 72 flow += DFS(S, INF); 73 } 74 return flow; 75 } 76 }sol; 77 void read(int &x){ 78 x = 0; int sig = 1; char ch = getchar(); 79 while(!isdigit(ch)) { if(ch == '-') sig = -1; ch = getchar(); } 80 while(isdigit(ch)) x = 10 * x + ch - '0', ch = getchar(); 81 x *= sig; return ; 82 } 83 void init(){ 84 read(n); read(m); 85 sol.init(n); 86 int u, v, w; 87 for(int i = 0; i < m; i++){ 88 read(u); read(v); read(w); 89 sol.AddEdge(u, v, w); 90 } 91 return ; 92 } 93 void work(){ 94 ans = sol.Max_Flow(1, n); 95 return ; 96 } 97 void print(){ 98 printf("%lld ", ans); 99 return ; 100 } 101 int main(){ 102 init(); 103 work(); 104 print(); 105 return 0; 106 }