很简单，感觉自己越来越适应数据结构题目了……

/*** 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* sortedArrayToBST(vector<int>& nums) {TreeNode* tree=new TreeNode(nums[nums.size()/2]);vector<int> left(nums.begin(),nums.begin()+nums.size()/2);vector<int> right(nums.begin()+nums.size()/2+1,nums.end());tree->left=sortedArrayToBST(left);tree->right=sortedArrayToBST(right);return tree;}
};