https://leetcode.com/problems/validate-binary-search-tree/

Author: harshitgindra

LeetCodeSolutions/BinarySearchTree/ValidateBinarySearchTree.cs

@@ -0,0 +1,49 @@
+namespace LeetCodeSolutions.BinarySearchTree
+{
+    class ValidateBinarySearchTree
+    {
+        public bool IsValidBST(TreeNode root)
+        {
+            // Use a more efficient approach with a single traversal
+            return IsValidBST(root, long.MinValue, long.MaxValue);
+        }
+
+        private bool IsValidBST(TreeNode node, long min, long max)
+        {
+            // Base case: empty trees are valid BSTs
+            if (node == null)
+            {
+                return true;
+            }
+
+            // Check if current node's value is within valid range
+            if (node.val <= min || node.val >= max)
+            {
+                return false;
+            }
+
+            // Recursively check left subtree (must be < node.Val) and right subtree (must be > node.Val)
+            return IsValidBST(node.left, min, node.val) &&
+                   IsValidBST(node.right, node.val, max);
+        }
+
+        [Test(Description = "https://leetcode.com/problems/validate-binary-search-tree/")]
+        [Category("Medium")]
+        [Category("LeetCode")]
+        [Category("Validate Binary Search Tree")]
+        [TestCaseSource(nameof(Input))]
+        [Category("Binary Search Tree")]
+        [Category("TopInterview")]
+        public void Test1((bool Output, int?[] Input) item)
+        {
+            var response = this.IsValidBST(item.Input.ToTreeNode());
+            Assert.That(response, Is.EqualTo(item.Output));
+        }
+
+        public static IEnumerable<(bool Output, int?[] Input)> Input =>
+            new List<(bool Output, int?[] Input)>()
+            {
+                (true, [2, 1, 3])
+            };
+    }
+}

README.md

@@ -137,11 +137,11 @@ The Top Interview 150 collection on Leetcode is a curated set of 150 interview q
 | 199                                         | Binary Tree Right Side View                                                                               | Medium     |    ✅    |
 | 83                                           | Average of Levels in Binary Tree                                                                          | Easy       |    ✅    |
 | 84                                           | Binary Tree Level Order Traversal                                                                         | Medium     |    ✅    |
-| 85                                           | Binary Tree Zigzag Level Order Traversal                                                                  | Medium     |        |
+| 103                                           | Binary Tree Zigzag Level Order Traversal                                                                  | Medium     |    ✅    |
 | <br>        Binary Search Tree<br>           |                                                                                                           |            |        |
 | 86                                           | Minimum Absolute Difference in BST                                                                        | Easy       |    ✅    |
 | 87                                           | Kth Smallest Element in a BST                                                                             | Medium     |        |
-| 88                                           | Validate Binary Search Tree                                                                               | Medium     |        |
+| 98                                           | Validate Binary Search Tree                                                                               | Medium     |   ✅     |
 | <br>        Graph General<br>                |                                                                                                           |            |        |
 | 89                                           | Number of Islands                                                                                         | Medium     |        |
 | 90                                           | Surrounded Regions                                                                                        | Medium     |        |