feat: update structure

cs2030s/labs/MockPE2/Main.java

@@ -0,0 +1,12 @@
+import java.util.stream.Stream;
+import java.util.List;
+import java.util.ArrayList;
+
+class Main {
+  public static String reverse(String s) {
+    return null;
+  }
+  public static Stream<String> palindrome(Stream<String> stream) {
+    return null;
+  }
+}