拓扑排序

1vector<int> topoSort(int n, vector<vector<int>>& adj) {
2    vector<int> indegree(n, 0);
3    for (int u = 0; u < n; u++)
4        for (int v : adj[u])
5            indegree[v]++;
6
7    queue<int> q;
8    for (int i = 0; i < n; i++)
9        if (indegree[i] == 0)
10            q.push(i);
11
12    vector<int> result;
13    while (!q.empty()) {
14        int u = q.front(); q.pop();
15        result.push_back(u);
16        for (int v : adj[u])
17            if (--indegree[v] == 0)
18                q.push(v);
19    }
20    return result; // 若 result.size() < n，则有环
21}