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Solution.cs
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27 lines (26 loc) · 770 Bytes
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/**
* Definition for a binary tree node.
* public class TreeNode {
* public int val;
* public TreeNode left;
* public TreeNode right;
* public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution
{
public bool IsValidBST(TreeNode root)
{
return IsValidBSTHelper(root, long.MinValue, long.MaxValue);
}
private bool IsValidBSTHelper(TreeNode root, long min, long max)
{
if (root == null) return true;
if (root.val <= min || root.val >= max) return false;
return IsValidBSTHelper(root.left, min, root.val) && IsValidBSTHelper(root.right, root.val, max);
}
}