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