Leetcode 210 Solution

class Solution {

public:
    vector<int> findOrder(int numCourses, vector<pair<int, int>>& prerequisites)
    {
        vector<int> degrees(numCourses);
        multimap<int, int> graph;

        for (auto pair : prerequisites)
        {
            degrees[pair.first]++;
            graph.insert(make_pair(pair.second, pair.first));
        }

        vector<int> res;
        queue<int> q;

        for (int i = 0; i < degrees.size(); i++)
        {
            if (degrees[i] == 0)
            {
                q.push(i);
                res.push_back(i);
            }
        }

        while (q.empty() == false)
        {
            int node = q.front();
            q.pop();

            for (auto it = graph.find(node); it != graph.end() && it->first == node; ++it)
            {
                degrees[it->second]--;

                if (degrees[it->second] == 0)
                {
                    q.push(it->second);
                    res.push_back(it->second);
                }
            }
        }

        return res.size() == numCourses ? res : vector<int>();
    }
};