class Solution {
    public int[] findOrder(int numCourses, int[][] prerequisites) {
        List<Integer> nodes = new ArrayList<>();
        for (int i = 0; i < numCourses; i++) nodes.add(i);

        HashMap<Integer, HashSet<Integer>> deps = new HashMap<>();

        for (int[] req: prerequisites) {
            deps.putIfAbsent(req[0], new HashSet<Integer>());
            deps.get(req[0]).add(req[1]);
        }

        List<Integer> res = new ArrayList<>();
        for (int v = 0; v < numCourses; v++) res.add(v);

        int[] result = new int[numCourses];
        for (int i = 0; i < numCourses; i++) result[i] = res.get(i);
        return result;
    }
}