feat: validate-binary-search-tree

Author: minji-go

validate-binary-search-tree/minji-go.java

@@ -0,0 +1,28 @@
+/**
+ * <a href="https://leetcode.com/problems/validate-binary-search-tree/">week02-5.validate-binary-search-tree</a>
+ * <li>Description: determine if it is a valid binary search tree (BST).    </li>
+ * <li>Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree    </li>
+ * <li>Time Complexity: O(N), Runtime 0ms       </li>
+ * <li>Space Complexity: O(N), Memory 43.25MB   </li>
+ */
+class Solution {
+    public boolean isValidBST(TreeNode root) {
+        return isValid(Integer.MIN_VALUE, Integer.MAX_VALUE, root);
+    }
+
+    public boolean isValid(long min, long max, TreeNode node) {
+        if(node == null) {
+            return true;
+        }
+
+        if (node.val < min || node.val > max) {
+            return false;
+        }
+
+        return isValid(min, (long) node.val - 1, node.left)
+            && isValid((long) node.val + 1, max, node.right);
+    }
+
+}
+
+