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
<思路>想要一个平衡二叉树就用递归的方法,每次取中间的点为root,左边为左子树,右边为右子树。
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def sortedArrayToBST(self, nums):
"""
:type nums: List[int]
:rtype: TreeNode
"""
return self.dfs(nums)
def dfs(self,nums):
if len(nums) == 0:
return
mid = len(nums) // 2
root = TreeNode(nums[mid])
root.left = self.dfs(nums[:mid])
root.right = self.dfs(nums[mid+1:])
return root