six seven

exam/packet.tex

@@ -141,5 +141,49 @@ Output:
 15 18
 \end{verbatim}
 
+% ========================= Problem 4 =========================
+\problem{Problem 3: Merge Intervals}
+\textit{Difficulty: Hard}
+
+You are given a string S composed of only the characters ‘6’, ‘7’, ‘A’, ‘B’, and ‘#’ (without the quotation marks). This string is processed from left to right, and you must maintain a sequence of chracters that changes according to these rules:
+1. The sequence starts out empty.
+2. 6 - add a 6 to the end of the sequences
+3. 7 - if the sequence is non-empty and its last chracter is ‘6’, remove that last ‘6’, otherwise, add ‘7’ to the end of the sequence
+4. A - reverse the sequence
+5. B - add a duplicate of the current sequence to the end of it
+6. # - clear the sequence
+
+\inputformat
+\begin{itemize}
+    \item The first line consists of the string S. The string consists only of the characters 6, 7, A, B, and #.
+    \item $|S|$ ($1 \leq n \leq 10^5$), the number of intervals.
+\end{itemize}
+
+\outputformat
+\begin{itemize}
+    \item Output a single line containig the final form of the sequence. If the sequence is empty at the end, output “EMPTY” (without the quotations).
+\end{itemize}
+
+\examples
+\begin{verbatim}
+Input 1:
+67A6
+
+Output 1:
+6
+
+Input 2:
+66B7
+
+Output 2:
+666
+
+Input 3:
+7A7#
+
+Output 3:
+EMPTY
+\end{verbatim}
+
 \end{document}