CourseScheduleII.txt

class Solution {
public:
    vector<int> findOrder(int numCourses, vector<vector<int>>& prerequisites) {
      //there is no weights 
        vector<int> adj[numCourses];
         vector<int> ans;
        for(int i=0;i<prerequisites.size();i++)
        {
            int x=prerequisites[i][0];
            int y=prerequisites[i][1];
            adj[y].push_back(x);
        }
        if(prerequisites.size()==0 && numCourses>0)
        {
            for(int i=0;i<numCourses;i++)
            {
                ans.push_back(i);
            }
            return ans;
        }
        //Now apply toposort using dfs
        queue<int> que;
        vector<int> indegree(numCourses,0);
        vector<int> topo;
        for(int i=0;i<prerequisites.size();i++)
        {
            indegree[prerequisites[i][0]]++;
        }
        for(int i=0;i<numCourses;i++)
        {
            if(indegree[i]==0)
            {
                que.push(i);
            }
        }
        while(!que.empty())
        {
            int x =que.front();
            que.pop();
            topo.push_back(x);
            for(auto it : adj[x])
            {
                    indegree[it]--;
                    if(indegree[it]==0)
                    que.push(it);
            }
        }
        if(topo.size()==numCourses)
        {
            return topo;
        }
        return ans;
        
    }
  
};