/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List
     
      
       > levelOrderBottom(TreeNode root) {        List
       
        
         > res=new ArrayList
         
          
           >(); if(root==null) return res; Queue
           
             q=new LinkedList
            
             (); q.offer(root); int size=q.size(); int count=0; List
             
               templist=new ArrayList
              
               (); while(!q.isEmpty()) { TreeNode temp=q.poll(); if(temp.left!=null) q.offer(temp.left); if(temp.right!=null) q.offer(temp.right); count++; templist.add(temp.val); if(count==size) { size=q.size(); count=0; res.add(templist); templist=new ArrayList
               
                (); } } List
                
                 
                  > revres=new ArrayList
                  
                   
                    >(); for(int i=res.size()-1;i>=0;i--) revres.add(res.get(i)); return revres; }}