courseschedule.cpp

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