How should I practice Validate a Strict Binary Search Tree?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Amazon phone screen problems in FastPrep.

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FastPrep tags this as a Amazon phone screen coding practice problem when the problem catalog has that company and stage context.

Validate a Strict Binary Search Tree

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Problem statement

Determine whether a binary tree is a binary search tree.

For this exercise, assume a strict BST: every value in a node's entire left subtree is smaller than that node's value, and every value in its entire right subtree is larger. Equal values are not allowed. An empty tree is valid.

Function

isStrictBST(root: TreeNode) → boolean

Examples

Example 1

root = [2,1,3]return = true

All left-subtree values are smaller and all right-subtree values are larger.

Example 2

root = [5,1,4,null,null,3,6]return = false

The right subtree contains 4 and 3, which violate the root bound 5.

Example 3

root = []return = true

For this exercise, the empty tree is valid.

Constraints

For this exercise, assume a finite acyclic binary tree containing 0 through 500 nodes.
-10^9 <= node.val <= 10^9.