solution.cpp

#include <bits/stdc++.h>
using namespace std;

class Solution
{
public:
    vector<int> findOrder(int numCourses, vector<vector<int>> &prerequisites)
    {
        vector<int> result;
        vector<int> fake;
        vector<int> degree(numCourses, 0);
        unordered_map<int, vector<int>> map;
        for (vector<int> prerequisite : prerequisites)
        {
            map[prerequisite[1]].push_back(prerequisite[0]);
            degree[prerequisite[0]]++;
        }
        queue<int> q;
        for (int i = 0; i < numCourses; i++)
        {
            if (degree[i] == 0)
            {
                q.push(i);
            }
        }
        while (!q.empty())
        {
            int cur = q.front();
            result.push_back(cur);
            q.pop();
            for (int next : map[cur])
            {
                degree[next]--;
                if (degree[next] == 0)
                    q.push(next);
            }
        }
        return result.size() == numCourses ? result : fake;
    }
};