leetcode429_N叉树的遍历

public List<List<Integer>> levelOrder(Node root) {
    List<List<Integer>> res = new ArrayList();
    if(root == null) return res;
    Deque<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();
            for(Node n: node.children) {
                if(n != null) q.offer(n);
            }
            list.add(node.val);
        }
        res.add(list);
    }
    return res;
}