# Validate Binary Search Tree

Validate Binary Search Tree tree

Given a binary tree, determine if it is a valid binary search tree (BST).

Assume a 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:
2
/ \
1   3
Binary tree [2,1,3], return true.
Example 2:
1
/ \
2   3
Binary tree [1,2,3], return false.
``````

Validate Binary Search Tree Solution

``````/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class ValidateBinarySearchTree {
public boolean isValidBST(TreeNode root) {
if(root == null) {
return true;
}

return validBSTRecursive(root, Long.MIN_VALUE, Long.MAX_VALUE);
}

public boolean validBSTRecursive(TreeNode root, long minValue, long maxValue) {
if(root == null) {
return true;
} else if(root.val >= maxValue || root.val <= minValue) {
return false;
} else {
return validBSTRecursive(root.left, minValue, root.val) && validBSTRecursive(root.right, root.val, maxValue);
}
}
}``````