DAY8P1.md

Validate Binary Search Tree

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• Question:

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.

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• Example:

Input: root = [2,1,3]

Output: true

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• Solution:

Code :

class Solution {
    TreeNode prev=null;
    public boolean isValidBST(TreeNode root) {
        if(root==null)
            return true;
        if(isValidBST(root.left)&&(prev==null|| root.val>prev.val))
        {
            prev=root;
            return isValidBST(root.right);
        }
        return false;
    }
}