题解 | #【模板】拓扑排序#

行末空格注意去掉（呃，奇奇怪怪）

#include<bits/stdc++.h>
using namespace std;
unordered_map<int, vector<int>>mp;
vector<int>ret;
queue<int> q;


int main()
{
    int n, m;
    cin >> n >> m;
    vector<int> v(n + 2, 0);
    
    while(m--)
    {
        int a, b;
        cin >> a >> b;
        mp[a].push_back(b);
        v[b]++;
    }
    for(int i = 1; i <= n; i++)
        if(v[i] == 0) q.push(i);
    
    while(q.size())
    {
        int t = q.front();
        q.pop();
        ret.push_back(t);
        for(auto i : mp[t])
            if(--v[i] == 0) q.push(i);
    }

    if(ret.size() < n) cout << -1 << endl;
    else
    {
        for(int i = 0; i < n; i++)
        {
            cout << ret[i];
            if(i == n - 1)cout << '\n';
            else cout << ' ';
        }
    }
    return 0;
}