LeetCode-Convert Sorted List to Binary Search Tree

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode *sortedListToBST(ListNode *head) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<int> vec;
while (head != NULL)
{
vec.push_back(head->val);
head = head->next;
}
return trans(vec, 0, vec.size() - 1);
}

TreeNode *trans(vector<int> &num, int left, int right)
{
if (left > right)
{
return NULL;
}
int mid = (left + right) >> 1;
TreeNode *ptr = new TreeNode(num[mid]);
ptr->left = trans(num, left, mid - 1);
ptr->right = trans(num, mid + 1, right);
return ptr;
}
};