108. 将有序数组转换为二叉搜索树

小鱼儿 2022-11-12 01:48 159阅读 0赞

**题目描述：**

给你一个整数数组 nums ，其中元素已经按 升序 排列，请你将其转换为一棵 高度平衡 二叉搜索树。

高度平衡 二叉树是一棵满足「每个节点的左右两个子树的高度差的绝对值不超过 1 」的二叉树。

**示例 1：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzI4MzM5Nw_size_16_color_FFFFFF_t_70_pic_center]

输入：nums = [-10,-3,0,5,9]
    输出：[0,-3,9,-10,null,5]
    解释：[0,-10,5,null,-3,null,9] 也将被视为正确答案

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzI4MzM5Nw_size_16_color_FFFFFF_t_70_pic_center 1]  
**示例 2：**  
![在这里插入图片描述][20210321222921418.png_pic_center]

输入：nums = [1,3]
    输出：[3,1]
    解释：[1,3] 和 [3,1] 都是高度平衡二叉搜索树。

**提示：**

*  1 <= nums.length <= 104
 *   − 1 0 4 < = n u m s \[ i \] < = 1 0 4 -10^4 <= nums\[i\] <= 10^4 −104<=nums\[i\]<=104
 *  nums 按 严格递增 顺序排列

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**解题思路:**

中序遍历，迭代生成左右子树

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**代码：**

# Definition for a binary tree node.
    # class TreeNode(object):
    #     def __init__(self, val=0, left=None, right=None):
    #         self.val = val
    #         self.left = left
    #         self.right = right
    class Solution(object):
        def sortedArrayToBST(self, nums):
            def helper(left, right):
                if left > right:
                    return None
                mid = (left + right) // 2
                root = TreeNode(nums[mid])
                root.left = helper(left, mid-1)
                root.right = helper(mid+1, right)
                return root
            return helper(0, len(nums)-1)

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**题目来源：**

[https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree/][https_leetcode-cn.com_problems_convert-sorted-array-to-binary-search-tree]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzI4MzM5Nw_size_16_color_FFFFFF_t_70_pic_center]: /images/20221022/d494d50e01844788b99ffe20aa8dc0e5.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzI4MzM5Nw_size_16_color_FFFFFF_t_70_pic_center 1]: https://img-blog.csdnimg.cn/20210321222851395.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzI4MzM5Nw==,size_16,color_FFFFFF,t_70#pic_center
[20210321222921418.png_pic_center]: https://img-blog.csdnimg.cn/20210321222921418.png#pic_center
[https_leetcode-cn.com_problems_convert-sorted-array-to-binary-search-tree]: https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree/