AtCoder Beginner Contest 223 D - Restricted Permutation（建图 思维 构造 拓扑排序）

// Problem: D - Restricted Permutation
// Contest: AtCoder - AtCoder Beginner Contest 223
// URL: https://atcoder.jp/contests/abc223/tasks/abc223_d
// Memory Limit: 1024 MB
// Time Limit: 2000 ms
// 
// Powered by CP Editor (https://cpeditor.org)
#include<iostream>
#include<cstdio> 
#include<string>
#include<ctime>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<sstream>
using namespace std;
typedef long long ll;
const int maxn=2e5+100;
int n,m,din[maxn];
vector<int>g[maxn],ans;
priority_queue<int,vector<int>,greater<int> >q;
int main() {
  cin>>n>>m;
  for(int i=1;i<=m;i++){
    int u,v;
    cin>>u>>v;
    g[u].push_back(v);
    g[v].push_back(u);
    din[v]++;
  }
  for(int i=1;i<=n;i++)
    if(!din[i]){
      q.push(i);
    }
  while(!q.empty()){
    int t=q.top();q.pop();
    ans.push_back(t);
    for(auto tt:g[t]){
      if(--din[tt]==0) q.push(tt);
    }
  }
  bool flag=0;
  for(int i=1;i<=n;i++)
    if(din[i]>0) flag=1;
  if(flag){
    puts("-1");return 0;
  }
  for(auto it:ans) cout<<it<<" ";
  return 0;
}