leetcode 210. Course Schedule II

class Solution {
public:
    vector<unordered_set<int>> makegraph(int numCourses, vector<pair<int, int>>& prerequisites){
        vector<unordered_set<int>> graph(numCourses);
        for(auto pre:prerequisites)
           graph[pre.second].insert(pre.first);
        return graph;
    }
    vector<int> deprees(vector<unordered_set<int>>& graph){
        vector<int> indeprees(graph.size(),0);
        for(auto g:graph)
           for(int a:g)
             indeprees[a]++;
        return indeprees;
    }
    vector<int> findOrder(int numCourses, vector<pair<int, int>>& prerequisites) {
        vector<int> res;
        vector<unordered_set<int>> graph=makegraph(numCourses,prerequisites);
        vector<int> indeprees=deprees(graph);
        int num=0;
        for(int i=0;i<indeprees.size();){
             if(!indeprees[i]){
                indeprees[i]=-1;
                res.push_back(i);
                num++;
                if(num==indeprees.size()) return res;
                for(int next:graph[i])
                   indeprees[next]--;
                i=0;
            }
            else i++;
        }
        return {};
    }
};