1 //裸拓扑排序，注意先输出比较小的数，使用优先队列即可
 2 #include <cstdio>
 3 #include <vector>
 4 #include <cstring>
 5 #include <queue>
 6 #include <algorithm>
 7 using namespace std;
 8 const int maxn = 505;
 9 vector<int> v[maxn];
10 priority_queue<int> q;
11 int f[maxn];
12 int main()
13 {
14     int n,m,x,y;
15     while(~scanf("%d%d",&n,&m))
16     {
17         memset(f,0,sizeof f);
18         for(int i = 1; i <= n; ++i)
19             v[i].clear();
20         while(m--)
21         {
22             scanf("%d%d",&x,&y);
23             v[x].push_back(y);
24             ++f[y];
25         }
26         for(int i = 1; i <= n; ++i)
27             if(f[i] == 0)
28                 q.push(-i);//默认大根堆
29         bool flag = true;
30         while(!q.empty())
31         {
32             int t = -q.top(); q.pop();
33             if(flag) { printf("%d",t); flag = false;}
34             else printf(" %d",t);
35             for(int i = 0; i < v[t].size(); ++i)
36                 if(!(--f[v[t][i]])) q.push(-v[t][i]);
37         }
38         printf("\n");
39     }
40     return 0;
41 }