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:
int dfs(TreeNode *root)
{
if(root==NULL) return 0;
if(root->left==NULL && root->right==NULL) return 1;
return max(dfs(root->left),dfs(root->right))+1;
}
void Ddfs(TreeNode *root,int t,vector<int> &vec,int step)
{
if(step==t) vec.push_back(root->val);
if(root->left)  Ddfs(root->left,t,vec,step+1);
if(root->right) Ddfs(root->right,t,vec,step+1);
}
vector<vector<int> > levelOrderBottom(TreeNode *root) {
int height=dfs(root);
vector<vector<int> > vec1;
for(int i=height;i>=1;i--)
{
vector<int> vec2;
Ddfs(root,i,vec2,1);
vec1.push_back(vec2);
}
return vec1;
}
};