HDU 3549 Flow Problem（最大流模板）

Posted 2020-09-02 谦谦君子，陌上其华

http://acm.hdu.edu.cn/showproblem.php?pid=3549

刚接触网络流，感觉有点难啊，只好先拿几道基础的模板题来练练手。

最大流的模板题。

 1 #include<iostream> 
 2 #include<cstring>
 3 #include<string>
 4 #include<algorithm>
 5 #include<queue>
 6 using namespace std;
 7 
 8 int n, m, flow;
 9 int vis[205];
10 //路径记录
11 int pre[205];
12 //邻接表
13 int G[205][205];
14 
15 void Maxflow()
16 {
17     for (;;)
18     {
19         memset(vis, 0, sizeof(vis));
20         memset(pre, 0, sizeof(pre));
21         queue<int> q;
22         q.push(1);
23         vis[1] = 1;
24         while (!q.empty())
25         {
26             int x = q.front();
27             q.pop();
28             //到达终点
29             if (x == n)  break;
30             for (int i = 1; i <= n; i++)
31             {
32                 if (!vis[i] && G[x][i] > 0)
33                 {
34                     vis[i] = 1;
35                     q.push(i);
36                     //记录好路径
37                     pre[i] = x;
38                 }
39             }
40         }
41         //没有找到增广路
42         if (!vis[n])  break;
43         int _min = 1000000;
44         for (int i = n; i != 1; i = pre[i])
45             _min = min(_min, G[pre[i]][i]);
46         for (int i = n; i != 1; i = pre[i])
47         {
48             G[i][pre[i]] += _min;
49             G[pre[i]][i] -= _min;
50         }
51         flow += _min;
52     }
53     return;
54 }
55 
56 int main()
57 {
58     //freopen("D:\\txt.txt", "r", stdin);
59     int T;
60     int u, v, w;
61     cin >> T;
62     for (int kase = 1; kase <= T; kase++)
63     {
64         cin >> n >> m;
65         memset(G, 0, sizeof(G));
66         for (int i = 0; i < m; i++)
67         {
68             cin >> u >> v >> w;
69             G[u][v] += w;
70         }
71         flow = 0;
72         Maxflow();
73         cout << "Case " << kase << ": " << flow << endl;
74     }
75 }