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\fancyhead[L]{Programming Competition Test}
\fancyhead[R]{\today}
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\newcommand{\problem}[1]{\section*{#1}}
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\newcommand{\outputformat}{\textbf{Output format:}}
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\begin{document}

\begin{center}
    {\LARGE \textbf{Programming Competition Test}}\\[2mm]
    {\large Duration: 2 hours \quad Total Marks: 100}
\end{center}

\section*{Instructions}
\begin{enumerate}[label=\arabic*.]
    \item This test contains algorithmic problems similar to those found on LeetCode or HackerRank.
    \item Use efficient algorithms to avoid timeouts; naive solutions may not receive full marks.
    \item Submit solutions in C++, Python, or Java.
    \item For each problem, write a function or program according to the specified input/output format.
    \item Clearly comment your code if necessary.
\end{enumerate}

% ========================= Problem 1 =========================
\problem{Problem 1: Two Sum}
\textit{Difficulty: Easy}

Given an array of integers \texttt{nums} and an integer \texttt{target}, return indices of the two numbers such that they add up to \texttt{target}. Assume exactly one solution exists.

\inputformat
\begin{itemize}
    \item First line contains an integer $n$ ($2 \leq n \leq 10^5$), the size of the array.
    \item Second line contains $n$ integers, the elements of the array.
    \item Third line contains the integer \texttt{target}.
\end{itemize}

\outputformat
\begin{itemize}
    \item Print two integers, the indices of the elements adding up to \texttt{target}.
\end{itemize}

\examples
\begin{verbatim}
Input:
4
2 7 11 15
9

Output:
0 1
\end{verbatim}

% ========================= Problem 2 =========================
\problem{Problem 2: Longest Substring Without Repeating Characters}
\textit{Difficulty: Medium}

Given a string \texttt{s}, find the length of the longest substring without repeating characters.

\inputformat
\begin{itemize}
    \item A single line containing the string \texttt{s} ($1 \leq |s| \leq 10^5$).
\end{itemize}

\outputformat
\begin{itemize}
    \item A single integer, the length of the longest substring without repeated characters.
\end{itemize}

\examples
\begin{verbatim}
Input:
abcabcbb

Output:
3
\end{verbatim}

% ========================= Problem 3 =========================
\problem{Problem 3: Merge Intervals}
\textit{Difficulty: Hard}

Given a collection of intervals, merge all overlapping intervals.

\inputformat
\begin{itemize}
    \item First line contains an integer $n$ ($1 \leq n \leq 10^4$), the number of intervals.
    \item Next $n$ lines contain two integers each, representing the start and end of each interval.
\end{itemize}

\outputformat
\begin{itemize}
    \item Print the merged intervals in ascending order of start times.
\end{itemize}

\examples
\begin{verbatim}
Input:
4
1 3
2 6
8 10
15 18

Output:
1 6
8 10
15 18
\end{verbatim}

% ========================= Problem 4 =========================
\problem{Problem 3: Merge Intervals}
\textit{Difficulty: Hard}
\begin{itemize}
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:

\item 6 - add a 6 to the end of the sequence
\item 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
\item A - reverse the sequence
\item B - add a duplicate of the current sequence to the end of it
\item \# - clear the sequence
\end{itemize}
\inputformat
\begin{itemize}
    \item The first line consists of the string S. The string consists only of the characters 6, 7, A, B, and \#.
\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}