Validate Binary Search Tree
Medium
Tree
Depth-First Search
Binary Search Tree
Binary Tree
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]
Output: true
Example 2
Input: root = [5,1,4,null,null,3,6]
Output: false
Example 3
Input: root = [1]
Output: true

Constraints

  • •The number of nodes in the tree is in the range [1, 10⁴].
  • •-2³¹ <= Node.val <= 2³¹ - 1
Time Complexity
O(n)
Space Complexity
O(h)
14
Case 1
Input: [2,1,3]
Expected: true
Case 2
Input: [5,1,4,null,null,3,6]
Expected: false
Case 3
Input: [1]
Expected: true