solves validate bst in java

Author: anishLearnsToCode

README.md

@@ -89,7 +89,7 @@
 |  95  | [Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii)                                                              |                                                            [![Java](assets/java.png)](src/UniqueBinarySearchTreesII.java)                                                            |                                                                                                                                   |
 |  96  | [Unique Binary Search Trees](https://leetcode.com/problems/unique-binary-search-trees)                                                                    |                                                             [![Java](assets/java.png)](src/UniqueBinarySearchTrees.java)                                                             |                                                                                                                                   |
 |  97  | [Interleaving String](https://leetcode.com/problems/interleaving-string)                                                                                  |                                                                                                                                                                                      |                                                                                                                                   |
-|  98  | [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree)                                                                  |                                                                                                                                                                                      |                                                                                                                                   |
+|  98  | [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree)                                                                  |                                                            [![Java](assets/java.png)](src/ValidateBinarySearchTree.java)                                                             |                                                                                                                                   |
 |  99  | [Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree)                                                                    |                                                                                                                                                                                      |                                                                                                                                   |
 | 100  | [Same Tree](https://leetcode.com/problems/same-tree)                                                                                                      |                                          [![Java](assets/java.png)](src/SameTree.java) [![Python](assets/python.png)](python/same_tree.py)                                           |                                                                                                                                   |
 | 101  | [Symmetric Tree](https://leetcode.com/problems/symmetric-tree)                                                                                            |                                     [![Java](assets/java.png)](src/SymmetricTree.java) [![Python](assets/python.png)](python/symmetric_tree.py)                                      |                                                                                                                                   |

src/ValidateBinarySearchTree.java

@@ -0,0 +1,17 @@
+// https://leetcode.com/problems/validate-binary-search-tree
+// T: O(n)
+// S: O(log(n))
+
+public class ValidateBinarySearchTree {
+    public boolean isValidBST(TreeNode root) {
+        return isValidBST(root, Long.MIN_VALUE, Long.MAX_VALUE);
+    }
+
+    private boolean isValidBST(TreeNode root, long minLeftVal, long maxRightVal) {
+        if (root == null) return true;
+        return minLeftVal < root.val
+                && root.val < maxRightVal
+                && isValidBST(root.left, minLeftVal, root.val)
+                && isValidBST(root.right, root.val, maxRightVal);
+    }
+}