CourseSchedule

void createGraph(vector<vector < int>> &pre, vector< vector< int>> &graph)
        {
            int e = pre.size();
            for (int i = 0; i < e; i++)
            {
                graph[pre[i][1]].push_back(pre[i][0]);
            }
        }
    bool finish(int n, vector<vector < int>> &prerequisites)
    {
       	// topological sort 
        vector<int> indeg(n, 0);
        vector<vector < int>> g(n, vector<int> (0));
        createGraph(prerequisites, g);
        int i;
        for (i = 0; i < prerequisites.size(); i++)
        {
            indeg[prerequisites[i][0]]++;
        }
        bool chk = false;
        queue<int> q;
        int cnt = 0;
        for (i = 0; i < n; i++)
        {
            if (indeg[i] == 0)
            {
                chk = 1;
                q.push(i);
                cnt++;
            }
        }
        if (chk)
        {
            while (!q.empty())
            {
                int n1 = q.front();
                q.pop();
                for (int i = 0; i < g[n1].size(); i++)
                {
                    indeg[g[n1][i]]--;
                    if (indeg[g[n1][i]] == 0)
                    {
                        q.push(g[n1][i]);
                        cnt++;
                    }
                }
            }
            if (cnt == n)
            {
                return true;
            }
        }
        return false;
    }
    bool canFinish(int n, vector<vector < int>> &prerequisites) 
    {
         return finish(n,prerequisites);
    }