## 题目地址

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

## 题目描述

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

``````Given the sorted array: [-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
``````

## 代码

``````class Solution {
public:
TreeNode* sortedArrayToBST(vector<int>& nums) {
return helper(nums, 0 , (int)nums.size() - 1);
}
TreeNode* helper(vector<int>& nums, int left, int right) {
if (left > right) return NULL;
int mid = left + (right - left) / 2;
TreeNode *cur = new TreeNode(nums[mid]);
cur->left = helper(nums, left, mid - 1);
cur->right = helper(nums, mid + 1, right);
return cur;
}
};
``````

``````class Solution {
public:
TreeNode* sortedArrayToBST(vector<int>& nums) {
if (nums.empty()) return NULL;
int mid = nums.size() / 2;
TreeNode *cur = new TreeNode(nums[mid]);
vector<int> left(nums.begin(), nums.begin() + mid), right(nums.begin() + mid + 1, nums.end());
cur->left = sortedArrayToBST(left);
cur->right = sortedArrayToBST(right);
return cur;
}
};
``````

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