恩，暴力解决。

参考了http://haipeng31.blog.163.com/blog/static/105623344201011984618863/

主要是changed变量的使用。

View Code 
 1 /*
 2 ID: xjtuacm1
 3 PROG: concom
 4 LANG: C++
 5 */
 6 #include<iostream>
 7 #include<stack>
 8 #include<cstring>
 9 #include<cstdio>
10 #include<queue>
11 #include<algorithm>
12 using namespace std;
13 
14 const int CMAX = 100 + 1;
15 
16 int comp[CMAX][CMAX];
17 bool owns[CMAX][CMAX];
18 
19 int main(int argc, char *argv[])
20 {
21     freopen("concom.in", "r", stdin);
22 #ifndef USACO
23     freopen("concom.out", "w", stdout);
24 #endif // USACO
25 
26     memset(comp, 0, sizeof(comp));
27     memset(owns, false, sizeof(owns));
28 
29     int n;
30     scanf("%d", &n);
31     while(n--)
32     {
33         int i, j;
34         scanf("%d %d", &i, &j);
35         scanf("%d", &comp[i][j]);
36     }
37 
38     for(int i = 0; i!= CMAX; i++)
39         owns[i][i] = true; // First condition
40 
41     for(int i = 0; i!= CMAX; i++)
42         for(int j = 0; j!= true; j++)
43             owns[i][j] = (comp[i][j] >= 50); // Second condition. This can be merged with third condition.
44 
45     bool changed = true;
46     while(changed)
47     {
48         changed = false;
49         for(int i = 1; i!= CMAX; i++)
50         {
51             for(int j = 1; j!= CMAX; j++)
52             {
53                 if(!owns[i][j])
54                 {
55                     int sum = 0;
56                     for(int k = 1; k!= CMAX; k++)
57                     {
58                         if(owns[i][k])
59                             sum += comp[k][j];
60                     }
61 
62                     if(sum >= 50)
63                     {
64                         owns[i][j] = true;
65                         changed = true;
66                     }
67                 }
68             }
69         }
70     }
71 
72     for(int i = 1; i!= CMAX; i++)
73     {
74         for(int j = 1; j!= CMAX; j++)
75         {
76             if(owns[i][j] && i!= j)
77                 printf("%d %d\n", i, j);
78         }
79     }
80 
81     return 0;
82 }

BTW，发现现在碰到暴力的题都有点儿不敢做了。。= =