将有序数组转换为二叉树
DescriptionExample题意解题思路code
108. Convert Sorted Array to Binary Search Tree Easy
Description
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
题意
将有序数组转化为对应的二叉树。
解题思路
求解树的问题应首先找出根结点，然后看能不能递归，如何递归实现。这题给定的是有序数组，那么对应的应该是一个先序遍历递增的二叉树，那么找到根结点后，根结点左边对应左子树，根结点右边对应右子树。
code
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
if len(nums) == 0:
return None
if len(nums) == 1:
return TreeNode(nums[0])
r = len(nums) // 2
root = TreeNode(nums[r])
root.left = self.sortedArrayToBST(nums[:r])
root.right = self.sortedArrayToBST(nums[r+1:])
return root
