[코테] 리트코드 트리 1038. Binary Search Tree to Greater Sum Tree

1038. Binary Search Tree to Greater Sum Tree

문제 링크

https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/description/

문제 설명

Given the root of a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus the sum of all keys greater than the original key in BST.

As a reminder, a binary search tree is a tree that satisfies these constraints:

• The left subtree of a node contains only nodes with keys less than the node’s key.
• The right subtree of a node contains only nodes with keys greater than the node’s key.
• Both the left and right subtrees must also be binary search trees.

제한 사항

• The number of nodes in the tree is in the range [1, 100].
• 0 <= Node.val <= 100
• All the values in the tree are unique.

입출력 예 #1

1. Input : root = [4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]
2. Output : [30,36,21,36,35,26,15,null,null,null,33,null,null,null,8]

입출력 예 #2

1. Input : root = [0,null,1]
2. Output : [1,null,1]

문제 풀이

중위 순회를 통해서 가장 오른쪽의 노드부터 가장 왼쪽 노드까지 누적합을 구하여 각 노드들의 값을 갱신한다.

class Solution:
    val: int = 0

    def bstToGst(self, root: TreeNode) -> TreeNode:
        # 중위 순회 노드 값 누적
        if root:
            self.bstToGst(root.right)
            self.val += root.val
            root.val = self.val
            self.bstToGst(root.left)

        return root