/**

  * 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<List<Integer>> levelOrderBottom(TreeNode root) {

         List<List<Integer>> list = new LinkedList<List<Integer>>();

         if(root == null) return list;

         Queue<TreeNode> queue1 = new LinkedList<TreeNode>();

         Queue<TreeNode> queue2 = new LinkedList<TreeNode>();

         queue1.offer(root);

         while(queue1.size()>0){

             List<Integer> childlist = new ArrayList<Integer>();

             while(queue1.size()>0){

                 TreeNode node = queue1.remove();

                 childlist.add(node.val);

                 if(node.left!=null) queue2.offer(node.left);

                 if(node.right!=null) queue2.offer(node.right);

             }

             list.add(0, childlist);

             Queue<TreeNode> temp = queue1;

             queue1 = queue2;

             queue2 = temp;

         }

         return list;

     }

 }