题解 | 【模板】拓扑排序

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

int main() {
    int n, m;
    cin >> n >> m;

    vector<vector<int>> graph(n + 1); // 邻接表（非矩阵）
    vector<int> indegress(n + 1, 0); // 记录结点入度

    for (int i = 0; i < m; ++ i) {
        int x, y;
        cin >> x >> y;
	  
        graph[x].push_back(y);
        ++indegress[y];
    }

    vector<int> ans;
    queue<int> q;
    for (int i = 1; i <= n; ++i) {
        if (indegress[i] == 0) {
            q.push(i);
            ans.push_back(i);
        }
    }

    while (!q.empty()) {
        int cur = q.front();
        q.pop();
        for (auto next : graph[cur]) {
			// 将入度为 0 的结点放入队列
            if (--indegress[next] == 0) {
                q.push(next);
                ans.push_back(next);
            }
        }
    }
	// 判断是否存在环
    if (ans.size() == n) {
        for (int i = 0; i < n; ++i) {
            cout << ans[i];
            if (i != n - 1) {
                cout << ' ';
            }
        }
    } else {
        cout << -1 << endl;
    }
}
// 64 位输出请用 printf("%lld")