Resolve build errors & cleanup structure (#2334)

Strings/ReverseString.java

@@ -0,0 +1,41 @@
+package Strings;
+
+/** Reverse String using different version */
+public class ReverseString {
+
+  public static void main(String[] args) {
+    assert reverse("abc123").equals("321cba");
+    assert reverse2("abc123").equals("321cba");
+  }
+
+  /**
+   * easiest way to reverses the string str and returns it
+   *
+   * @param str string to be reversed
+   * @return reversed string
+   */
+  public static String reverse(String str) {
+    return new StringBuilder(str).reverse().toString();
+  }
+
+  /**
+   * second way to reverses the string str and returns it
+   *
+   * @param str string to be reversed
+   * @return reversed string
+   */
+  public static String reverse2(String str) {
+
+    if (str == null || str.isEmpty()) {
+      return str;
+    }
+
+    char[] value = str.toCharArray();
+    for (int i = 0, j = str.length() - 1; i < j; i++, j--) {
+      char temp = value[i];
+      value[i] = value[j];
+      value[j] = temp;
+    }
+    return new String(value);
+  }
+}