wayetan
1/3/2014 - 8:06 AM

## Validate Binary Search Tree

Validate Binary Search 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.
*/

/**
* Definition for binary tree
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/

public class Solution {
public boolean isValidBST(TreeNode root) {
if(root == null) return true;
if(root.left == null && root.right == null) return true;
return isBSTUtil(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
}

public boolean isBSTUtil(TreeNode root, int min, int max) {
if (root == null)
return true;
return (root.val > min && root.val < max && isBSTUtil(root.left, min, root.val) && isBSTUtil(root.right, root.val, max));
}
}
``````