class Solution {
public List<List<Integer>> levelOrder(Node root) {
if (root == null)
return new ArrayList<>();
List<List<Integer>> res = new ArrayList<>();
Queue<Node> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()){
int size = queue.size();
List<Integer> layer = new ArrayList<>();
for (int i=0;i<size;i++){
Node tmp = queue.poll();
layer.add(tmp.val);
queue.addAll(tmp.children);
}
res.add(layer);
}
return res;
}
}