//BFS solution
//Time: O(n), 6ms
//Space: O(n)
class Solution {
    public List<List<Integer>> levelOrder(Node root) {
        List<List<Integer>> ans = new ArrayList<>();
        if(root == null) return ans;
        Queue<Node> q = new LinkedList<>();
        q.offer(root);
        while(!q.isEmpty()) {
            int size = q.size();
            List<Integer> list = new ArrayList<>();
            for(int i = 0; i < size; i++) {
                Node node = q.poll();
                list.add(node.val);
                for(Node child : node.children) {
                    q.offer(child);
                }
            }
            ans.add(list);
        }
        return ans;
    }
}
/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val,List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/