Course Schedule II LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> findOrder(int numCourses, vector<vector<int>> &prerequisites) {
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    map<int, vector<int>> adj;
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    vector<int> indegree(numCourses, 0);
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    vector<int> res;
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    for (int i = 0; i < prerequisites.size(); i++) {
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      adj[prerequisites[i][1]].push_back(prerequisites[i][0]);
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      indegree[prerequisites[i][0]]++;
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    }
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    queue<int> q;
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    for (int i = 0; i < numCourses; i++) {
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      if (indegree[i] == 0) q.push(i);
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    }
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    while (!q.empty()) {
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      int x = q.front();
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      q.pop();
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      res.push_back(x);
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      for (auto u : adj[x]) {
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        indegree[u]--;
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        if (indegree[u] == 0) {
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          q.push(u);
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        }
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      }
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    }
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    if (res.size() == numCourses) return res;
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    return {};
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  }
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};