### LeetCode Challenge #98. Validate Binary Search Tree

Given the `root` of a binary tree, determine if it is a valid binary search tree (BST).

valid BST is defined as follows:

• The left

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`
##### Video Solution
###### Java Solution
```				```
class Solution {
public boolean isValidBST(TreeNode root) {
return helper(root, Long.MIN_VALUE , Long.MAX_VALUE);
}

public boolean helper(TreeNode root , long min , long max ){
if(root==null){
return true ;
}

if(root.val<=min || root.val>=max){
return false ;
}

boolean leftAns = helper(root.left , min , root.val);
boolean rightAns = helper(root.right , root.val , max );
return leftAns && rightAns ;
}
}
```
```