用到了优先队列以保证字典序最小！！！

#include<iostream>
#include<vector>
#include<stack>
#include <queue>
using namespace std;

vector<vector<int>> graph;
vector<int> ans;
priority_queue<int, vector<int>, greater<int>> s;
int* indegree;
int n,m;

int main(){
    cin>>n>>m;
    graph.resize(n+1);
    indegree=new int[n+1]();
    
    for(int i=0;i<m;i++)
    {
        int u,v;
        cin>>u>>v;
        graph[u].push_back(v);
        indegree[v]++;
    }
    
    for(int i=1;i<=n;i++)
    {
        if(indegree[i]==0) s.push(i);
    }
    
    int count=0;
    while(!s.empty())
    {
        int u=s.top();
        s.pop();
        ans.push_back(u);
        count++;
        for(int v:graph[u])
        {
            indegree[v]--;
            if(indegree[v]==0) s.push(v);
        }
    }

    if(count!=n) cout<<-1<<"\n";
    else
    {
        for(int i:ans)
        {
            cout<<i<<" ";
        }
    }
    delete[] indegree;
    return 0;
}