LintCode-剑指Offer-(69)二叉树的层次遍历

class Solution {    /**    * @param root: The root of binary tree.    * @return: Level order a list of lists of integer    */public:    //写了一个非递归的，发现内存不够用。。。    void lev(TreeNode* node, int levelnum, vector<vector<int>>&v){        if ( node == NULL )return;        if ( v.size( ) <= levelnum )            v.push_back(vector<int>( ));        v[levelnum].push_back(node->val);        lev(node->left,levelnum+1,v);        lev(node->right,levelnum+1,v);    }    vector<vector<int>> levelOrder(TreeNode *root) {        // write your code here        vector<vector<int>> vall;        if ( root == NULL )            return vall;        lev(root, 0, vall);        return vall;    }};