leetcode 102. 二叉树的层次遍历

			

 /**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
      if(!root)return  vector<vector<int>>();
      vector<vector<int>>ans;
      queue<TreeNode*>q;
      q.push(root);
      while(!q.empty())
      {
        vector<int>temp;
        int rec=q.size();
        for(int i=0;i<rec;i++)
        {
        TreeNode* res=q.front();
        temp.push_back(res->val);
        q.pop();
        if(res->left)q.push(res->left);
        if(res->right)q.push(res->right);       
        }
        ans.push_back(temp);  
      }
      
      return ans;
    }
};