/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution
{
public boolean isValidBST(TreeNode root)
{
if(root==null)
return true;
return isValidBST(root, 0, 0, false, false);
}
public boolean isValidBST(TreeNode root, int min, int max, boolean minValid, boolean maxValid)
{
if((minValid==true)&&(root.val<=min))
return false;
if((maxValid==true)&&(root.val>=max))
return false;
boolean left = true;
boolean right = true;
if(root.left!=null)
left = isValidBST(root.left, min, root.val, minValid, true);
if(root.right!=null)
right = isValidBST(root.right, root.val, max, true, maxValid);
return (left & right);
}
}