A more efficient version of the Java 606

Author: Zanger67

Diff for: my-submissions/m606 v2 String Builder.java

@@ -0,0 +1,38 @@
+/**
+ * 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 String tree2str(TreeNode root) {
+        return helper(root, new StringBuilder()).toString();
+    }
+
+    public StringBuilder helper(TreeNode curr, StringBuilder sb) {
+        sb.append(curr.val);
+
+        if (curr.left != null) {
+            sb.append("(");
+            helper(curr.left, sb);
+            sb.append(")");
+        } else if (curr.right != null) {
+            sb.append("()");
+        }
+        if (curr.right != null) {
+            sb.append("(");
+            helper(curr.right, sb);
+            sb.append(")");
+        }
+        return sb;
+    }
+}