POJ3660-Permutations-传递闭包FLOYD

 1 #include "cstdio"
 2 #include "iostream"
 3 #include "cstring"
 4 using namespace std;
 5 int  E[105][105];
 6 int main()
 7 {
 8     int n , m;
 9     cin >> n >> m;
10     memset(E, 0, sizeof(E));
11     for (int i = 1 ; i <= n ; i++)
12     {
13         E[i][i] = 1;
14     }
15     for (int i = 1 ; i <= m; i++)
16     {
17         int a, b;
18         scanf("%d%d", &a, &b);
19         E[a][b] = 1;
20     }
21     for (int k = 1; k <= n ; k++)
22         for (int i = 1; i <= n ; i++)
23             for (int j = 1; j <= n ; j++)
24                 if ((E[i][k]) && (E[k][j])) E[i][j] = 1;
25 
26     int ans = 0, j;
27     for (int i = 1 ; i <= n ; i++)
28     {
29         for( j = 1; j <= n; j++)
30             if (E[i][j] + E[j][i] == 0) break;
31         if (j > n) ans++;
32     }
33     cout << ans << endl;
34 }