動機

複習dfs

Problem

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one.

 

Example 1:

Input: nums = [-10,-3,0,5,9]Output: [0,-3,9,-10,null,5]Explanation: [0,-10,5,null,-3,null,9] is also accepted:

Example 2:

Input: nums = [1,3]Output: [3,1]Explanation: [1,3] and [3,1] are both a height-balanced BSTs.

 

Constraints:

  • 1 <= nums.length <= 104
  • -104 <= nums[i] <= 104
  • nums is sorted in a strictly increasing order.

Sol

class Solution:
    def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
        if not nums:
            return None
        else:
            mid = len(nums)//2
            ret = TreeNode(nums[mid])
            ret.left = self.sortedArrayToBST(nums[:mid])
            ret.right = self.sortedArrayToBST(nums[mid+1:])
            return ret