LC-1038 Medium LeetCode

1038. Binary Search Tree to Greater Sum Tree

Tree Depth-First Search Binary Search Tree Binary Tree

Read the full problem statement on LeetCode.

Difficulty: medium Acceptance: 88% Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree

Reading material

Reference solution (spoiler · python)

# Time:  O(n)
# Space: O(h)

# Definition for a binary tree node.
class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution(object):
    def bstToGst(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        def bstToGstHelper(root, prev):
            if not root:
                return root
            bstToGstHelper(root.right, prev)
            root.val += prev[0]
            prev[0] = root.val
            bstToGstHelper(root.left, prev)
            return root
        
        prev = [0]
        return bstToGstHelper(root, prev)

Solution from kamyu104/LeetCode-Solutions · MIT