题目：

题解：

class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return helper(nums, 0, nums.size() - 1);
    }

    TreeNode* helper(vector<int>& nums, int left, int right) {
        if (left > right) {
            return nullptr;
        }

        // 选择任意一个中间位置数字作为根节点
        int mid = (left + right + rand() % 2) / 2;

        TreeNode* root = new TreeNode(nums[mid]);
        root->left = helper(nums, left, mid - 1);
        root->right = helper(nums, mid + 1, right);
        return root;
    }
};