LeetCodeを1日1題解いてみる (day21)

21日目に取り組んだ問題はこちら！

108. Convert Sorted Array to Binary Search Tree

問題文

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

僕の回答 (失敗作)

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sortedArrayToBST(self, nums: List[int]) -> Optional[TreeNode]:
        mid = len(nums) // 2
        left_arr = nums[:mid]
        right_arr = nums[mid:]
        node = TreeNode(nums[mid])
        root = node     

回答例

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sortedArrayToBST(self, nums: List[int]) -> Optional[TreeNode]:
        if not nums:
            return None
        
        def buildBST(left: int, right: int) -> Optional[TreeNode]:
            if left > right:
                return None
            mid = (left + right) // 2
            node = TreeNode(nums[mid])

            node.left = buildBST(left, mid - 1)
            node.right = buildBST(mid + 1, right)

            return node
        
        return buildBST(0, len(nums) - 1)

コメント

こんな感じなのかな、というのは掴めるがそれを具体的にアルゴリズムとコードに落とし込むことが苦手です。

次の問題はこちら!