Convert Sorted List to Binary Search Tree

Example:

Given the sorted linked list: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     /    -3   9
   /   /
 -10  5

class Solution
{
public:
    TreeNode* sortedListToBST(ListNode* head)
    {
        if(head==nullptr)
            return nullptr;

        vector<int> res;
        auto tmp=head;
        while(tmp)
        {
            res.emplace_back(tmp->val);
            tmp=tmp->next;
        }
        return dfs(0,res.size()-1,res);
    }
private:
    TreeNode *dfs(int start,int end,vector<int>& res)
    {
        if(end<start)
            return nullptr;

        int index=(start+end)/2;
        TreeNode *root=new TreeNode(res.at(index));
        root->left=dfs(start,index-1,res);
        root->right=dfs(index+1,end,res);

        return root;
    }
};