Leetcode 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]
]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

vector<vector<int> > levelOrderBottom(TreeNode *root) {
    vector<vector<int> > result;
    if(root == NULL) return result;
    queue<TreeNode *> que;
    que.push(root);
    while(!que.empty()){
        vector<int> row;
        int cnt = que.size();
        while(cnt--){
            TreeNode *node = que.front();que.pop();
            row.push_back(node->val);
            if(node->left)  que.push(node->left);
            if(node->right) que.push(node->right);
        }
        result.push_back(row);
    }
    reverse(result.begin(),result.end());
    return result;
}