course schedule

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

        vector<int>id(numCourses),ans;
        map<int,vector<int>>mp;
        for(auto v:prerequisites){
            id[v[0]]++;
            mp[v[1]].push_back(v[0]);
        }
        queue<int>q;
        for(int i=0;i<id.size();i++){
            if(id[i]==0)q.push(i);
        }
        int cnt=0;
        while(!q.empty()){
            int x=q.front();
            ans.push_back(x);
            q.pop();
            for(auto v:mp[x]){
                id[v]--;
                if(id[v]==0)q.push(v);
            }
            cnt++;
        }
        if(cnt!=numCourses)return {};
        return ans;
    }
};