# Leetcode 98 - Validate BST

`Note:`

- Use
`inorder`

traversal. - If a tree is a BST, then its
`inorder`

traversal would be a`strictly increasing array`

.

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

A valid 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 | Input: root = [2,1,3] |

1 | /** |