131. Validate Binary Search Tree

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Example 1:

Input: root = [2,1,3]

Output: true

Explanation: The tree is a valid BST because 1 < 2 < 3.

Example 2:

Input: root = [5,1,4,null,null,3,6]

Output: false

Explanation: The tree is not a valid BST because the node with value 4 has a left child with value 3, which violates the BST property (3 should be less than 4).

Constraints:

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Time Complexity

O(n)

Space Complexity

O(h)