Add Cryptic Letter playground assignment

Author: 100yo

playground/04-cryptic-letter/README.md

@@ -0,0 +1,49 @@
+## Загадъчно писмо :secret:
+
+Това мистериозно послание в код пристигна по пощата една сутрин. Разбираш ли нещо?
+
+```java
+public class LetterDecoder {
+
+    /**
+     * Ava J. sent you a letter for your secret annual meeting.
+     * You must decode it to understand when the meeting will take place.
+     * Ava never makes mistakes when writing her letters. If you ever see one, consider that a clue.
+     * <p>
+     * The first 3 letters of Ava's letters always represents the *month*. Be sure of that.
+     * <p>
+     * Decode the exact *hour* of the meeting by counting the number of hidden paragraphs.
+     * If you see a punctuation mistake that would mean the end of a hidden paragraph. *1*
+     * If you count more that 24 hours, something is not quite right.
+     * <p>
+     * Decode the exact *minutes* of the meeting by counting the number of misplaced symbols.
+     * For every misplaced symbol add 5 minutes. *2*
+     * If you count more than 60 minutes, something is not quite right.
+     * <p>
+     * Decode the exact *day* of the month Ava wants you to meet her by counting the length
+     * of the hidden paragraph which starts with the word "The" (including a period at the end). *3,4*
+     * <p>
+     * *1* - Ava would never make punctuation mistakes.
+     * Normally every sentence in her letters ends with one occurrence of a period, no more no less.
+     * *2* - Ava would never replace letters from the alphabet with symbols.
+     * Normally she writes S instead of $.
+     * *3* - Ava would never start a hidden paragraph with the word "The".
+     * *4* - Ava would never leave a lot of unnecessary space between the hidden paragraphs.
+     * Either at the start, or the end.
+     *
+     * @param message The coded message that Ava sent you.
+     * @return decoded Message in the format [*day* *month* at *hour*:*minutes*], e.g. "17th October at 9:00".
+     * Print "Maybe another *time*" if you feel something is not right.
+     * (Replace *time* with the reason you think the meeting might not happen,
+     * е.g. "Maybe another day" or "Maybe another minute").
+     * If the message is empty, print "Maybe another day".
+     */
+    public String decodeMessage(final String message) {
+        // TBD: replace with your solution
+        return null;
+    }
+
+}
+```
+
+Напомня ми за една случка от *A Series of Unfortunate Events*.

playground/README.md

@@ -7,3 +7,4 @@
 | 01 | [Stock Exchange](https://github.com/fmi/java-course/tree/master/playground/01-stock-exchange) | масиви, цикли, алгоритми |
 | 02 | [DNA Analyzer](https://github.com/fmi/java-course/tree/master/playground/02-dna-analyzer) | низове, цикли, алгоритми |
 | 03 | [Dungeons](https://github.com/fmi/java-course/tree/master/playground/03-dungeons) | ООП, низове, цикли |
+| 04 | [Cryptic Letter](https://github.com/fmi/java-course/tree/master/playground/04-cryptic-letter) | низове, цикли |