按之字形顺序打印二叉树

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
//仍然是层序遍历的思想进行改进
class Solution {
public:
    vector<vector<int> > Print(TreeNode* pRoot) {
         queue<TreeNode *>que;
         vector<vector<int> >res;
         if(pRoot==NULL)
               return res;
         int flag = false;
         que.push(pRoot);
         while(!que.empty())
          {
             int size = que.size();
             vector<int>vec;
             for(int i=0;i<size;++i)
             {
                TreeNode *tmp = que.front();
                que.pop();
                vec.push_back(tmp->val);
                if(tmp->left)
                     que.push(tmp->left);
                if(tmp->right)
                      que.push(tmp->right);
             }

             if(flag)
                  reverse(vec.begin(),vec.end());
             res.push_back(vec); 
             flag = !flag;
          }
        return res;
       }     
};