LeetCode刷题笔记（107，二叉树的层次遍历2，Easy）

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List> levelOrderBottom(TreeNode root) {
        List> result = new ArrayList<>();
        if(root == null){
            return result;
        }
        Queue q = new LinkedList<>();
        q.add(root);
        while(!q.isEmpty()){
            List demo = new ArrayList<>();
            int queuelength = q.size();
            for(int i=0;i