class Solution {
    public int[] findOrder(int numCourses, int[][] prerequisites) {

        // Step 1: Create adjacency list
        ArrayList<ArrayList<Integer>> adj = new ArrayList<>();
        for(int i = 0; i < numCourses; i++)
            adj.add(new ArrayList<>());

        // Step 2: fill adjacency list and indegree array
        int[] indegree = new int[numCourses];
        for(int[] edge : prerequisites)
        {
            int prereq = edge[1];
            int course = edge[0];

            adj.get(prereq).add(course);
            indegree[course]++;
        }

        // Step 3: Queue for nodes with indegree 0
        Queue<Integer> q = new LinkedList<>();

        for(int i = 0; i < numCourses; i++)
            if(indegree[i] == 0)
                q.add(i);

        // Step 4: Topological Sort
        int[] ans = new int[numCourses];
        int index = 0;

        while(!q.isEmpty())
        {
            int node = q.poll();
            ans[index++] = node;

            for(int next : adj.get(node))
            {
                indegree[next]--;
                if(indegree[next] == 0)
                    q.add(next);
            }
        }

        // Cycle check
        if(index != numCourses)
            return new int[0];

        return ans;
    }
}