Binary Tree Level Order Traversal II

貌似快速AC一道题的效果还不如怎么都AC不了呢

https://leetcode.com/problems/binary-tree-level-order-traversal-ii/

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List<List<Integer>> levelOrderBottom(TreeNode root) {          LinkedList<List<Integer>> ret = new LinkedList<List<Integer>>();        if(root==null) return ret;        Queue<TreeNode> q=new LinkedList<TreeNode>();        q.offer(root);        while(!q.isEmpty()){            int cnt = q.size();            LinkedList<Integer> tmp=new LinkedList<Integer>();            for(int i = 0 ; i < cnt ; i++){            TreeNode head = q.poll();                    tmp.add(head.val);                    if(head.left != null)                        q.offer(head.left);                    if(head.right != null)                        q.offer(head.right);                    }            ret.addFirst(tmp);                    }        return ret;    }}