Validate Binary Search Tree: coding question

Problem

You get the root root of a binary tree. In a binary tree, each node has at most two children: a left child and a right child.

Return true if the tree is a valid binary search tree (BST). Otherwise, return false.

The left subtree of a node is its left child and all the nodes below that child. The right subtree of a node is its right child and all the nodes below that child.

In a valid BST, each node meets two rules. All values in its left subtree are smaller than the node value. All values in its right subtree are larger than the node value.

The examples show each tree as a list in level order. This list gives the nodes row by row, from left to right. The value null marks a missing child.

Example 1

Input:: root = [10,5,15]
Output:: true

Example 2

Input:: root = [10,5,15,null,null,8,20]
Output:: false
Explanation:: Node 8 is in the right subtree of the root 10, but 8 is smaller than 10.

Example 3

Input:: root = [7,7]
Output:: false
Explanation:: The left child has the same value as the root. A value in the left subtree must be smaller.

Constraints

1 <= number of nodes <= 10^4
-2^31 <= Node.val <= 2^31 - 1

SysRound wrote this statement. A reference solution checks every example.

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Amazon
Leetcode 98. Validate Binary Search Tree
Reported Aug 3, 2026 · 2 source reports
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Microsoft
Leetcode 98. Validate Binary Search Tree
Reported Jan 17, 2026 · 1 source report
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Lyft
Validate Binary Search Tree
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Lyft
Validate Binary Search Tree

Problem

You get the root root of a binary tree. In a binary tree, each node has at most two children: a left child and a right child.

Return true if the tree is a valid binary search tree (BST). Otherwise, return false.

The left subtree of a node is its left child and all the nodes below that child. The right subtree of a node is its right child and all the nodes below that child.

In a valid BST, each node meets two rules. All values in its left subtree are smaller than the node value. All values in its right subtree are larger than the node value.

The examples show each tree as a list in level order. This list gives the nodes row by row, from left to right. The value null marks a missing child.

Example 1

Input:: root = [10,5,15]
Output:: true

Example 2

Input:: root = [10,5,15,null,null,8,20]
Output:: false
Explanation:: Node 8 is in the right subtree of the root 10, but 8 is smaller than 10.

Example 3

Input:: root = [7,7]
Output:: false
Explanation:: The left child has the same value as the root. A value in the left subtree must be smaller.

Constraints

1 <= number of nodes <= 10^4
-2^31 <= Node.val <= 2^31 - 1

SysRound wrote this statement. A reference solution checks every example.

Validate Binary Search Tree

Problem

Example 1

Example 2

Example 3

Constraints

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Validate Binary Search Tree

Problem

Example 1

Example 2

Example 3

Constraints

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