/*

 struct TreeNode {

     int val;

     struct TreeNode *left;

     struct TreeNode *right;

     TreeNode(int x) :

             val(x), left(NULL), right(NULL) {

     }

 };

 */

 class Solution {

 public:

     vector<vector<int> > Print(TreeNode* pRoot) {

         vector<vector<int> > res;

         if(pRoot == NULL) return res;

         stack<TreeNode*> s1, s2;

         s1.push(pRoot);

         while() {

             vector<int> v1;

             while(!s1.empty()) {

                 TreeNode* top = s1.top();

                 v1.push_back(top->val);

                 if(top->left) s2.push(top->left);

                 if(top->right) s2.push(top->right);

                 s1.pop();

             }

             res.push_back(v1);

             if(s2.empty()) break;

             vector<int> v2;

             while(!s2.empty()) {

                 TreeNode* top = s2.top();

                 v2.push_back(top->val);

                 if(top->right) s1.push(top->right);

                 if(top->left) s1.push(top->left);

                 s2.pop();

             }

             res.push_back(v2);

             if(s1.empty()) break;

         }

         return res;

     }

 };