Day8-9

98. Validate Binary Search Tree/Solution.cs

@@ -0,0 +1,21 @@
+namespace _98._Validate_Binary_Search_Tree;
+
+public class Solution
+{
+    public bool IsValidBST(TreeNode root)
+    {
+        return Rec(root, null, null);
+    }
+
+    private bool Rec(TreeNode node, int? lessThan, int? moreThan)
+    {
+        if((lessThan != null && node.val >= lessThan) || (moreThan != null && node.val <= moreThan))
+            return false;
+        bool res = true;
+        if(node.left != null)
+            res&=Rec(node.left, node.val, moreThan);
+        if(node.right != null)
+            res &=Rec(node.right, lessThan, node.val);
+        return res;
+    }
+}