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Validate Binary Search Tree

Check whether a binary tree follows the search-tree ordering rule.

MediumTrees

Given the root of a binary tree, decide whether it is a valid binary search tree (BST).

In a valid BST, a node's left subtree contains only values strictly less than the node's value, its right subtree contains only values strictly greater, and both subtrees are valid BSTs themselves.

Examples

Example 1
Input
root = [2, 1, 3]
Output
true
Example 2
Input
root = [5, 1, 4, null, null, 3, 6]
Output
false
Why
The root is 5, but its right child 4 is smaller than 5.

Constraints

  • The tree has between 1 and 10^4 nodes.
  • -2^31 <= Node.val <= 2^31 - 1