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 }
