dinic弧优化 P3376 【模板】网络最大流 

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 typedef long long ll;
 4 const int N = 1000;
 5 ll dep[N], h[N], now[N],n, m, s, t, ee = 2;
 6 
 7 struct edge{
 8     ll v, next, flow;
 9 }e[10010];
10 void addedge(int u, int v, int flow)
11 {
12     e[ee] = (edge){v, h[u], flow};
13     h[u] = ee++;
14 }
15 ll bfs()
16 {
17     memset(dep, -1, sizeof(dep));
18     queue<ll>q;
19     q.push(s);
20     dep[s] = 0;
21     now[s] = h[s];
22     while (q.size())
23     {
24         ll u = q.front();
25         q.pop();
26         for(int i = h[u]; i; i = e[i].next)
27         {
28             ll v = e[i].v;
29             if(dep[v] == -1 && e[i].flow > 0)
30             {
31                 dep[v] = dep[u] + 1;
32                 now[v] = h[v];
33                 q.push(v);
34                 if(v == t)return 1;
35             }
36         }
37     }
38     return 0;
39 }
40 
41 ll dfs(ll u, ll path_misum)
42 {
43     if(u == t)return path_misum;
44     ll ans = 0;
45     for(int i = now[u]; i && path_misum; i = e[i].next)
46     {    
47         now[u] = i; 
48         ll v = e[i].v;
49         if(dep[v] == dep[u] + 1 && e[i].flow > 0)
50         {
51             ll other_flow = dfs(v, min(e[i].flow, path_misum));
52             e[i].flow -= other_flow;
53             e[i ^ 1].flow += other_flow;
54             ans += other_flow;
55             path_misum -= other_flow; 
56             
57         }
58     }
59     return ans;
60 }
61 ll dinic()
62 {
63     ll ans = 0;
64     while (bfs())
65     {
66         ans += dfs(s, LONG_MAX);
67     }
68     return ans;
69 }
70 int main()
71 {
72     ios::sync_with_stdio(false);cin.tie(0);
73     cin >> n >> m >> s >> t;
74     ll u, v, flow;
75     for(int i = 1; i <= m; i++)
76     {
77         cin >> u >> v >> flow;
78         addedge(u, v, flow);
79         addedge(v, u, 0);
80     }
81     cout << dinic() << "\n";
82     return 0;
83 }

 

posted @ 2022-05-03 23:07  matt-11  阅读(32)  评论(0)    收藏  举报