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1373. Maximum Sum BST in Binary Tree

{leetcode}/problems/maximum-sum-bst-in-binary-tree/[LeetCode - 1373. Maximum Sum BST in Binary Tree ^]

Given a binary tree root, return the maximum sum of all keys of any sub-tree which is also a Binary Search Tree (BST).

Assume a BST is defined as follows:

  • 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.

Example 1:

<img alt="" src="https://assets.leetcode.com/uploads/2020/01/30/sample_1_1709.png" style="width: 320px; height: 250px;" />

Input: root = [1,4,3,2,4,2,5,null,null,null,null,null,null,4,6]
Output: 20
Explanation: Maximum sum in a valid Binary search tree is obtained in root node with key equal to 3.

Example 2:

<img alt="" src="https://assets.leetcode.com/uploads/2020/01/30/sample_2_1709.png" style="width: 134px; height: 180px;" />

Input: root = [4,3,null,1,2]
Output: 2
Explanation: Maximum sum in a valid Binary search tree is obtained in a single root node with key equal to 2.

Example 3:

Input: root = [-4,-2,-5]
Output: 0
Explanation: All values are negatives. Return an empty BST.

Constraints:

  • The number of nodes in the tree is in the range [1, 4 * 104].

  • -4 * 104 ⇐ Node.val ⇐ 4 * 104

思路分析

一刷
link:{sourcedir}/_1373_MaximumSumBstInBinaryTree.java[role=include]

参考资料