Binary Tree Level Order Traversal II

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        stack<vector<int> > mystack;
        deque<TreeNode *> queue;
        deque<TreeNode *> prequeue;
        if(root!=NULL)
        queue.push_back(root);
        vector<vector<int> > result;
        vector<int> temp;
        while(queue.size())
        {
            temp.clear();
            prequeue = queue;
            queue.clear();
            for(deque<TreeNode *>::iterator iter = prequeue.begin();iter!=prequeue.end();iter++)
            {
                temp.push_back((*iter)->val);
                if((*iter)->left!=NULL)
                queue.push_back((*iter)->left);
                if((*iter)->right!=NULL)
                queue.push_back((*iter)->right);
            }
            mystack.push(temp);
        }
        while(!mystack.empty())
        {
            result.push_back(mystack.top());
            mystack.pop();
        }
        return result;
    }
};