feat: #230 add java solution

problems/230.kth-smallest-element-in-a-bst.md

@@ -56,6 +56,8 @@ What if the BST is modified (insert/delete operations) often and you need to fin
 
 解法一：
 
+JavaScript Code:
+
 ```js
 
 
@@ -107,9 +109,44 @@ var kthSmallest = function(root, k) {
 };
 ```
 
+Java Code:
+
+```java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+private int count = 1;
+private int res;
+
+public int KthSmallest (TreeNode root, int k) {
+    inorder(root, k);
+    return res;
+}
+
+public void inorder (TreeNode root, int k) {
+    if (root == null) return;
+
+    inorder(root.left, k);
+
+    if (count++ == k) {
+        res = root.val;
+        return;
+    }
+
+    inorder(root.right, k);
+}
+```
 
 解法二：
 
+JavaScript Code:
+
 ```js
 
 /**