refactor 538

Author: fishercoder1534

Diff for: README.md

@@ -111,7 +111,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |541|[Reverse String II](https://leetcode.com/problems/reverse-string-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_541.java) | O(n) |O(1) | Easy | String
 |540|[Single Element in a Sorted Array](https://leetcode.com/problems/single-element-in-a-sorted-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_540.java) | O(n) |O(1) | Medium | 
 |539|[Minimum Time Difference](https://leetcode.com/problems/minimum-time-difference/)|[Solution](../master/src/main/java/com/fishercoder/solutions/MinimumTimeDifference.java) | O(n) |O(1) | Medium | String
-|538|[Convert BST to Greater Tree](https://leetcode.com/problems/convert-bst-to-greater-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_538.java) | O(n) |O(h) | Medium | Tree
+|538|[Convert BST to Greater Tree](https://leetcode.com/problems/convert-bst-to-greater-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_538.java) | O(n) |O(h) | Easy | Tree
 |537|[Complex Number Multiplication](https://leetcode.com/problems/complex-number-multiplication/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_537.java) | O(1) |O(1) | Medium | Math, String
 |536|[Construct Binary Tree from String](https://leetcode.com/problems/construct-binary-tree-from-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_536.java) | O(n) |O(h) | Medium | Recursion, Stack
 |535|[Encode and Decode TinyURL](https://leetcode.com/problems/encode-and-decode-tinyurl/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_535.java) | O(1) |O(n) | Medium | Design

Diff for: src/main/java/com/fishercoder/solutions/_538.java

@@ -29,16 +29,18 @@
 public class _538 {
 
     public static class BSTSolution {
-        /**reference: https://discuss.leetcode.com/topic/83455/java-recursive-o-n-time/13
-         *
-         * A reversed version of inorder traversal: right -> root -> left*/
+        /**
+         * Traverse in this order: right -> root -> left
+         */
         public TreeNode convertBST(TreeNode root) {
             dfs(root, 0);
             return root;
         }
 
         private int dfs(TreeNode root, int val) {
-            if (root == null) return val;
+            if (root == null) {
+                return val;
+            }
             int right = dfs(root.right, val);
             root.val += right;
             int left = dfs(root.left, root.val);
@@ -85,4 +87,5 @@ private void putNodeToList(List<Integer> list, TreeNode root) {
             if (root.right != null) putNodeToList(list, root.right);
         }
     }
-}
+
+}