Resolve build errors & cleanup structure (#2334)

Strings/Alphabetical.java

@@ -0,0 +1,33 @@
+package Strings;
+
+/**
+ * Alphabetical order is a system whereby character strings are placed in order based on the
+ * position of the characters in the conventional ordering of an alphabet. Wikipedia:
+ * https://en.wikipedia.org/wiki/Alphabetical_order
+ */
+class Alphabetical {
+
+  public static void main(String[] args) {
+    assert !isAlphabetical("123abc");
+    assert isAlphabetical("aBC");
+    assert isAlphabetical("abc");
+    assert !isAlphabetical("xyzabc");
+    assert isAlphabetical("abcxyz");
+  }
+
+  /**
+   * Check if a string is alphabetical order or not
+   *
+   * @param s a string
+   * @return {@code true} if given string is alphabetical order, otherwise {@code false}
+   */
+  public static boolean isAlphabetical(String s) {
+    s = s.toLowerCase();
+    for (int i = 0; i < s.length() - 1; ++i) {
+      if (!Character.isLetter(s.charAt(i)) || !(s.charAt(i) <= s.charAt(i + 1))) {
+        return false;
+      }
+    }
+    return true;
+  }
+}