LeetCode 108: Convert Sorted to Binary Search Tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
	TreeNode *go(vector<int>& nums, int start, int end) {
		if (start > end) return NULL;
		int mid = (start + end) / 2;
		TreeNode * root = new TreeNode(nums[mid]);
		root->left = go(nums, start, mid - 1);
		root->right = go(nums, mid + 1, end);
		return root;
	}
	TreeNode *sortedArrayToBST(vector<int>& nums) {
		if (!nums.size()) return NULL;
		return go(nums, 0, nums.size() - 1);
	}
};