feat: lowest-common-ancestor-of-a-binary-search-tree

Author: minji-go

kth-smallest-element-in-a-bst/minji-go.java

@@ -0,0 +1,31 @@
+/**
+ * <a href="https://leetcode.com/problems/kth-smallest-element-in-a-bst/">week13-3. kth-smallest-element-in-a-bst</a>
+ * <li>Description: Given the root of a binary search tree, and an integer k, return the kth smallest value</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(H), Memory 44.5MB</li>
+ * <li>Note: if the BST is modified often,  
+ */
+class Solution {
+    public int kthSmallest(TreeNode root, int k) {
+        return inorder(root, new AtomicInteger(k));
+    }
+
+    public Integer inorder(TreeNode node, AtomicInteger k) {
+        if (node == null) {
+            return null;
+        }
+
+        Integer value = inorder(node.left, k);
+        if (value != null) {
+            return value;
+        }
+
+        if (k.decrementAndGet() == 0) {
+            return node.val;
+        }
+
+        return inorder(node.right, k);
+    }
+
+}