Binary Tree Level Order Traversal II

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int> >res;
int maxDepth(TreeNode *root){
if(!root) return 0;
return max(maxDepth(root->left),maxDepth(root->right))+1;
}
void dfs(TreeNode *root,int level){
if(!root) return;
res[level].push_back(root->val);
dfs(root->left,level-1);
dfs(root->right,level-1);
}
vector<vector<int> > levelOrderBottom(TreeNode *root) {
int depth = maxDepth(root);
if(!depth) return res;
for(int i = 0 ; i < depth ; i++){//开始时没初始化一直run error,vector不会啊。。。
res.push_back(vector<int>());
}
dfs(root,depth-1);
return res;
}
};