POJ2594 Treasure Exploratio —— 最小路径覆盖 + 传递闭包

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <string>
 6 #include <vector>
 7 #include <map>
 8 #include <set>
 9 #include <queue>
10 #include <sstream>
11 #include <algorithm>
12 using namespace std;
13 const int INF = 2e9;
14 const int MOD = 1e9+7;
15 const int MAXN = 500+10;
16 
17 int n;
18 int M[MAXN][MAXN], link[MAXN];
19 bool vis[MAXN];
20 
21 bool dfs(int u)
22 {
23     for(int i = 1; i<=n; i++)
24     if(M[u][i] && !vis[i])
25     {
26         vis[i] = true;
27         if(link[i]==-1 || dfs(link[i]))
28         {
29             link[i] = u;
30             return true;
31         }
32     }
33     return false;
34 }
35 
36 int hungary()
37 {
38     int ret = 0;
39     memset(link, -1, sizeof(link));
40     for(int i = 1; i<=n; i++)
41     {
42         memset(vis, 0, sizeof(vis));
43         if(dfs(i)) ret++;
44     }
45     return ret;
46 }
47 
48 void Flyod()
49 {
50     for(int k = 1; k<=n; k++)
51         for(int i = 1; i<=n; i++)
52             for(int j = 1; j<=n; j++)
53                 M[i][j] = M[i][j]|(M[i][k]&&M[k][j]);
54 }
55 
56 int main()
57 {
58     int m;
59     while(scanf("%d%d", &n, &m) && (n||m))
60     {
61         memset(M, false, sizeof(M));
62         for(int i = 1; i<=m; i++)
63         {
64             int u, v;
65             scanf("%d%d", &u, &v);
66             M[u][v] = true;
67         }
68 
69         Flyod();    //求出传递闭包
70         int cnt = hungary();
71         printf("%d\n", n-cnt);
72     }
73 }