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
        vector<vector<int> > r;
        queue<TreeNode *> q,p,useless;
        
        
        
        TreeNode * t;   
        if(root==NULL)
            return r;
            
        q.push(root);
        
        while(!q.empty())
        {
             vector<int> v;
             while(!q.empty())
             {
                
                t=q.front();
                v.push_back(t->val);
                q.pop();
                if(t->left)
                    p.push(t->left);
                if(t->right)
                    p.push(t->right);
            }
            q=p;
            p=useless;
            r.push_back(v);
        }
        
        reverse(r.begin(),r.end());
       
        
        
        return r;
    }
};