HDU 1532 Drainage Ditches

http://acm.hdu.edu.cn/showproblem.php?pid=1532

基础题。

 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         queue<int> q;
21         q.push(1);
22         vis[1] = 1;
23         while (!q.empty())
24         {
25             int x = q.front();
26             q.pop();
27             //到达终点
28             if (x == m)  break;
29             for (int i = 1; i <= m; i++)
30             {
31                 if (!vis[i] && G[x][i] > 0)
32                 {
33                     vis[i] = 1;
34                     q.push(i);
35                     //记录好路径
36                     pre[i] = x;
37                 }
38             }
39         }
40         //没有找到增广路
41         if (!vis[m])  break;
42         int _min = 1000000;
43         for (int i = m; i != 1; i = pre[i])
44             _min = min(_min, G[pre[i]][i]);
45         for (int i = m; i != 1; i = pre[i])
46         {
47             G[i][pre[i]] += _min;
48             G[pre[i]][i] -= _min;
49         }
50         flow += _min;
51     }
52 }
53
54 int main()
55 {
56     //freopen("D:\\txt.txt", "r", stdin);
57     while (cin >> n >> m)
58     {
59         int u, v, w;
60         memset(G, 0, sizeof(G));
61         for (int i = 0; i < n; i++)
62         {
63             cin >> u >> v >> w;
64             //因为可能存在重边的情况
65             G[u][v] += w;
66         }
67         flow = 0;
68         Maxflow();
69         cout << flow << endl;
70     }
71 }