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Validate Binary Search Tree

Given the root of a binary tree, determine whether it is a valid binary search tree: every node in a left subtree is strictly less than its ancestor, every node in a right subtree strictly greater, and all subtrees are themselves valid.

Constraints

1 ≤ number of nodes ≤ 10^4
-2^31 ≤ node value ≤ 2^31 - 1

Examples

in: root = [2,1,3]

out: true

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

out: false

Node 3 sits in the right subtree of 5.

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