剑指offer 分行从上到下打印二叉树

题目：

从上到下按层打印二叉树，同一层的节点按照从左到右的顺序打印，每一层打印到一行。

 /*
 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* root) {
         vector<vector<int> > res;
         vector<int> v;
         if (root == NULL)
             return res;
         TreeNode* temp;
         queue<TreeNode*> q;
         q.push(root);
         while(!q.empty()) {
             v.clear();
             int len = q.size(); //队列中的元素个数即为当前行的所有元素
             v.resize(len, );
             for (int i = ; i < len; i++) {
                 temp = q.front();
                 q.pop();
                 v[i] = temp->val;
                 if (temp->left != NULL)
                     q.push(temp->left);
                 if (temp->right != NULL)
                     q.push(temp->right);
             }
             res.push_back(v);
         }
     }
 };