Merge pull request neetcode-gh#160 from r1cky0/patch-6

Create 230-Kth-Smallest-Element-in-a-BST.java

Author: neetcode-gh

java/230-Kth-Smallest-Element-in-a-BST.java

@@ -0,0 +1,30 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    public int kthSmallest(TreeNode root, int k) {
+        List<Integer> list = new ArrayList<>();
+        inorder(root, list);
+        return list.get(k - 1);
+    }
+    
+    private void inorder(TreeNode root, List<Integer> list) {
+        if (root == null) return;
+        
+        inorder(root.left, list);
+        list.add(root.val);
+        inorder(root.right, list);
+    }
+}