1 #include
     
       2 using namespace std; 3 void DFS(int**mat, int *mark,int *sp, int n, int p) 4 { 5     int i; 6     //DFS每个顶点 7     if(!mark[p]) 8     for(i=1;i<=n;i++) 9         if (mat[p][i]&&i!=p)//
      
       10         {11             mark[p] = 1;12             sp[p] = 1;13             DFS(mat,mark,sp, n, i);14             mark[p] = 0;15         }16 }17 int main()18 {19     int n, m,i,j; cin >> n >> m;20     int**mat = new int*[n+1];21     for (i = 0; i <= n; i++)22         mat[i] = new int[n+1];23     for (i = 0; i <= n; i++)24         for (j = 0; j <= n; j++)25             mat[i][j] = 0;26     int a, b;27     for (i = 0; i < m; i++)28     {29         cin >> a >> b;30         mat[a][b] = 1;31     }32     int *mark = new int[n + 1];33     int *sp = new int[n + 1];34     int sum = 0,k;35     for (i = 1; i <= n; i++)36         mark[i] = 0;37     for (i = 1; i < n; i++)38     {39         for (k = 1; k <= n; k++)40             sp[k] = 0;41         DFS(mat, mark, sp, n, i);42         for (j = i + 1; j <= n; j++)43         {44             if (sp[j])//
       
        45             {46                 for (k = 1; k <= n; k++)47                     sp[k] = 0;48                 DFS(mat, mark, sp, n, j);49                 if (sp[i])//
        
         50                     sum++;51             }52         }53     }54     cout << sum << endl;55     return 0;56 }