1 class Solution {
2 public List<List<Integer>> levelOrderBottom(TreeNode root) {
3 Queue<TreeNode> queue = new LinkedList<>();
4 List<List<Integer>> res = new ArrayList<>();
5 if(root == null) return res;
6 queue.offer(root);
7 int size = queue.size();
8 List<Integer> list = new ArrayList<>();
9 while(!queue.isEmpty()) {
10 for(int i = 0; i < size; i++) {
11 TreeNode node = queue.poll();
12 list.add(node.val);
13 if(node.left != null) {
14 queue.offer(node.left);
15 }
16 if(node.right != null) {
17 queue.offer(node.right);
18 }
19 }
20 size = queue.size();
21 res.add(0, list);
22 list = new ArrayList<>();
23 }
24 return res;
25 }
26 }
