Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its bottom-up level order traversal as:

[
  [15,7],
  [9,20],
  [3]
]

/**
 * 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;
        List<Integer> intList = new LinkedList<Integer>();
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        TreeNode t = null;
        queue.offer(root);
        int curCount=0,curNum=1,nextCount=1;
        while(!queue.isEmpty()){
        	t=queue.poll();
        	intList.add(t.val);
        	if(t.left!=null){
        		queue.offer(t.left);
        		nextCount++;
        	}if(t.right!=null){
        		queue.offer(t.right);
        		nextCount++;
        	}
        	if(++curCount==curNum){
        		list.add(0,intList);
        		intList=new LinkedList<Integer>();
        		curNum=nextCount;
        	}
        }return list;
    }
}