course_schedule_II.cpp

class Solution {
public:
    vector<int> findOrder(int numCourses, vector<vector<int>>& prerequisites) {
        vector<vector<int>> graph(numCourses);
        vector<int> indegree(numCourses, 0);

        for(int i = 0; i < prerequisites.size(); i++){
            int pre = prerequisites[i][1];
            int course = prerequisites[i][0];

            graph[pre].push_back(course);
            indegree[course]++;
        }

        queue<int> q;
        
        for(int i = 0; i < numCourses; i++){
            if(indegree[i] == 0)
                q.push(i);
        }

        vector<int> result;

        while(!q.empty()){
            int curr = q.front();
            q.pop();

            result.push_back(curr);

            for(int next : graph[curr]){
                if(--indegree[next] == 0)
                    q.push(next);
            }
        }

        if(result.size() == numCourses)
            return result;
        else
            return {};
    }
};