Binary Tree Level Order Traversal II

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,#,#,15,7}

,

3
/ \
9  20
/  \
15   7

return its bottom-up level order traversal as:

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

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int> > levelOrderBottom(TreeNode *root) {
vector<vector<TreeNode*> > list;
vector<vector<int> > result;
if(root==NULL)
return result;
vector<TreeNode*> level;
level.push_back(root);
list.push_back(level);
while(level.size()>0)
{
vector<TreeNode*> newlevel;
for(int i=0;i<level.size();i++)
{
if(level[i]->left!=NULL) newlevel.push_back(level[i]->left);
if(level[i]->right!=NULL) newlevel.push_back(level[i]->right);
}
list.push_back(newlevel);
level=newlevel;
}

for(int i=0;i<list.size()-1;i++)
{
vector<int> v;
for(int j=0;j<list[list.size()-i-2].size();j++)
v.push_back(list[list.size()-i-2][j]->val);
result.push_back(v);
}
return result;
}
};