LeetCode 1038. Binary Search Tree to Greater Sum Tree

파이썬 알고리즘 인터뷰 51번(리트코드 1038번) Binary Search Tree to Greater Sum Tree
https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/

나의 풀이

# 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 bstToGst(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        curr = 0
        def helper(root):
            nonlocal curr
            if not root:
                return
            helper(root.right)
            root.val, curr = root.val + curr, curr + root.val
            helper(root.left)
        helper(root)
        return root

다른 풀이1

# 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:
    val = 0
    def bstToGst(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if root:
            self.bstToGst(root.right)
            self.val += root.val
            root.val = self.val
            self.bstToGst(root.left)
        return root

다른 풀이2

# 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 bstToGst(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        def helper(root, curr):
            if not root:
                return curr
            root.val += helper(root.right, curr)
            return helper(root.left, root.val)
        helper(root, 0)
        return root