class Solution {
public boolean isValidBST(TreeNode root) {
return isValidBST(root, null, null);
}
private boolean isValidBST(TreeNode root, TreeNode minNode, TreeNode maxNode) {
if (root == null)
return true;
if (minNode != null && root.val <= minNode.val)
return false;
if (maxNode != null && root.val >= maxNode.val)
return false;
return isValidBST(root.left, minNode, root) &&
isValidBST(root.right, root, maxNode);
}
}
leetcode
challenge
here is the link for the problem:
https://leetcode.com/problems/validate-binary-search-tree/submissions/
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