Validate Binary Search Tree Leetcode Solution

In this post, we are going to solve the Validate Binary Search Tree Leetcode Solution problem of Leetcode. This Leetcode problem is done in many programming languages like C++, Java, and Python.

Table of Contents

Problem

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
Explanation: The root node's value is 5 but its right child's value is 4.

Constraints:

The number of nodes in the tree is in the range [1, 10⁴].
-2³¹ <= Node.val <= 2³¹ - 1

Now, let’s see the leetcode solution of Validate Binary Search Tree Leetcode Solution.

Validate Binary Search Tree Leetcode Solution in Python

class Solution:
  def isValidBST(self, root: Optional[TreeNode]) -> bool:
    def isValidBST(root: Optional[TreeNode],
                   minNode: Optional[TreeNode], maxNode: Optional[TreeNode]) -> bool:
      if not root:
        return True
      if minNode and root.val <= minNode.val:
        return False
      if maxNode and root.val >= maxNode.val:
        return False

      return isValidBST(root.left, minNode, root) and \
          isValidBST(root.right, root, maxNode)

    return isValidBST(root, None, None)

Validate Binary Search Tree Leetcode Solution in CPP

class Solution {
 public:
  bool isValidBST(TreeNode* root) {
    return isValidBST(root, nullptr, nullptr);
  }

 private:
  bool isValidBST(TreeNode* root, TreeNode* minNode, TreeNode* maxNode) {
    if (root == nullptr)
      return true;
    if (minNode && root->val <= minNode->val)
      return false;
    if (maxNode && root->val >= maxNode->val)
      return false;

    return isValidBST(root->left, minNode, root) &&
           isValidBST(root->right, root, maxNode);
  }
};

Validate Binary Search Tree Leetcode Solution in Java

class Solution {
  public boolean isValidBST(TreeNode root) {
    return isValidBST(root, null, null);
  }

  private boolean isValidBST(TreeNode root, TreeNode minNode, TreeNode maxNode) {
    if (root == null)
      return true;
    if (minNode != null && root.val <= minNode.val)
      return false;
    if (maxNode != null && root.val >= maxNode.val)
      return false;

    return isValidBST(root.left, minNode, root) &&
           isValidBST(root.right, root, maxNode);
  }
}

Note: This problem Validate Binary Search Tree is generated by Leetcode but the solution is provided by Chase2learn This tutorial is only for Educational and Learning purposes.

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