Leetcode Problem 1373. Maximum Sum BST in Binary Tree
Leetcode Solutions
Postorder Traversal and BST Validation
- Define a helper function that returns a tuple containing the sum of the subtree, the maximum and minimum values within the subtree, and a boolean indicating whether it's a valid BST.
- Perform a postorder traversal (left, right, root).
- At each node, get the results from the left and right subtrees.
- Check if the current node's value is greater than the maximum value of the left subtree and less than the minimum value of the right subtree.
- If the current subtree is a valid BST, calculate its sum and update the maximum sum found so far.
- Return the sum, maximum, minimum, and validity of the current subtree.
- If the current subtree is not a valid BST, return the sum as 0 and mark it as invalid.
- After the traversal, return the maximum sum found.
In-Order Traversal with Global State
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