将二叉树从叶节点到根节点输出

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
import java.util.*;
public class Solution {
    public ArrayList<ArrayList<Integer>> levelOrderBottom(TreeNode root) {
        ArrayList<ArrayList<Integer>> lists = new ArrayList<>();
        if(root==null)
            return lists;
       Queue<TreeNode> q = new LinkedList<>();
       q.add(root);
        while(!q.isEmpty()){
            int n = q.size();
            ArrayList<Integer> list = new ArrayList<>();
            while(n>0){
            TreeNode temp = q.poll();
            list.add(temp.val);
            if(temp.left!=null)
                q.add(temp.left);
            if(temp.right!=null)
                q.add(temp.right);
                n--;
            }
            lists.add(list);
        }
        for(int i=0;i<lists.size()/2;i++){
            ArrayList<Integer> temp = lists.get(i);
            lists.set(i,lists.get(lists.size()-i-1));
            lists.set(lists.size()-i-1,temp);              
        }
        return lists;
    }
}