Semper Opera House
Faculty of Informatics


CEOI 2008 is over. The winner is Goran Zuzic of Croatia - Congratulations! For further information, please consult the results table.


Problem descriptions of all 6 tasks can be downloaded here.

Test Cases

Test cases for all 6 tasks can be downloaded here (26 MB).

We also provide separate downloads for each task.

Some files contain a special grader.


You can see the short version of the solution description of all 6 tasks here.

CEOI Regulations

The current version of the regulations was approved by the General Assembly at CEOI 2007 in Brno, Czech Republic.

CEOI 2008 Competition Rules

These Competition Rules cover Competition Procedures and Judging Procedures. These Rules are not final, changes may be made and will be announced explicitly as such, and the final version will be distributed at the first GA meeting of CEOI 2008. Delegation Leaders have the responsibility of ensuring that all members of their delegation fully understand these rules and abide by them.

Changes since the first announcement


All of the tasks in CEOI 2008 are designed to be algorithmic in nature. Efficiency plays an important role in some tasks. Whenever efficiency of an algorithm is important, test cases will be designed to differentiate between solutions with different levels of efficiency; the smallest test cases will be designed so that any reasonable correct solution for the tasks can solve them within the task constraints. Therefore, it is worthwhile to attempt a task even if the contestant does not know how to solve large test cases within the constraints.
Tasks may be of the following types:

For every task a memory limit will be specified. This limit is on the overall memory usage including executable code size, a stack, a heap, etc.

Batch tasks

The source program provided by the contestant must be contained in a single source file. The task statement will define:

Reactive tasks

The source program provided by the contestant must be contained in a single source file. The task statement will specify:

Output-only tasks

The competition might include tasks for which input data is given to the contestant and the contestant is required to produce only the output data as a solution. If the contestant writes programs to help determine the output data, the programs must not be submitted with the solution. The input data will be provided in ASCII text files. For these tasks, the task statement will specify:

Input and output data

In all tasks, input and output data consist of one or more lines, each ending with an end-of-line character, including the last line. The end-of-line character in Linux is represented by the single character '\n' (ASCII code 10). Each line contains one or more space-separated items. An item is a string of printable non-white-space characters (ASCII code from 33 through 126, inclusive). An item may represent an integer or a general string; the meaning of each item will be given in the task description.
The format and limits for input and output data will be specified in the task description. The output data should be formatted strictly according to the task-specific instructions. The exact amount and type of whitespace you use to separate the elements in the output file will not matter in most cases as long as kept to a minimum. However, it is recommended to follow the output specification as precisely as possible.

Competition Procedures

Competition Schedule

There will be two competition days. On each competition day contestants will be given three tasks to complete in the five hours. The schedule will be published on the official competition web site.
There will also be a two hour Practice Competition prior to the first competition day. The purpose of this practice round is to familiarize all participants with the environment and procedures, all contestants are encouraged to take part in the Practice Competition round.


In order to protect the confidentiality of the tasks, all direct and indirect contacts and communication between contestants and delegation leaders are prohibited between the moment where tasks for a competition day are presented to the members of the GA and the end of the five-hour round on the following day. During this period the contestants are not allowed to communicate by any means, direct or indirect, with any member of the GA or anyone who has seen the tasks. The GA members are not allowed to communicate task-related information to anyone who is not a member of the GA. The contestants, the GA members and anyone else who has had access to the tasks must obey any instructions which restrict their access to specific parts of the CEOI venue.
If a contestant violates the quarantine, he or she can be subject to disqualification. If some other person associated with a national delegation violates the quarantine, then all contestants of that delegation can be subjects to disqualification.

Competition Equipment and Environment

All contest machines will be installed to boot in Linux. Microsoft Windows will not be available in the contest machines. The following packages will be installed:

Hardware specification:

In order to translate tasks, team leaders will be provided with computers with a text editor with some multi-language support. In addition, network access will be available for leaders bringing laptops.

Competition Supplies

In the competition room, blank paper and writing utensils will be provided. On the competition days, contestants may not bring anything into the competition rooms, but:

If a contestant wants to bring a keyboard or mouse, small mascots or English dictionaries to the competition, these must be submitted to the technical staff during the practice competition day. Any of these will be checked and, if cleared, will be given to the contestant in the first competition day. After the first competition day, the contestant must leave these items on his or her workstation if he or she wants to use them during the second competition day. Once again these will be checked and, if cleared, will be given to the contestant in the second competition day. After the second competition day the contestant must take any of these items with him or her.
Any attempt to bring any other item into the competition room will be considered cheating. In particular, during competition rounds it is strictly prohibited to bring:

Any electronic or printed materials provided by the organizers during the Competition Round may be used by the contestants (e.g., a Users Guide to the Contest System, or any electronic documentation or reference manuals provided in the installed contest environment or on the provided Contest Server).

Starting the Competition

On the competition days, immediately after breakfast ends, contestants will be admitted to the competition hall. All contestants must bring their ID badges to the competition. Each contestant will have a pre-assigned workstation; this information will be posted in the morning of the competition day. Contestants should be in their seats by at least 5 minutes prior to the start of the competition. On the way to their computers contestants will be checked to verify that they are only bringing allowed items into the competition hall. Small mascots and dictionaries must be submitted to the technical staff during the practice competition day, check Competition supplies section. Contestants must find their assigned computer, sit down, and wait for the competition to begin without touching any:

The beginning of the competition will be marked by an audible start signal, after which the contestant may use any of the above items.

Clarification Requests

During the first two hours of competition, contestants may submit written questions concerning any ambiguities or items needing clarification in the competition tasks. Questions must be submitted on the provided Clarification Request Forms, expressed either in the contestant's native language or in English. If required, delegation leaders will translate their contestants' questions into English after they are submitted and before they are sent to the Scientific Committee. The Scientific Committee will respond to every question submitted by the contestants. Since this might take some time, contestants should continue working while waiting for the answer to their questions. Contestants should phrase their questions so that a yes/no answer will be meaningful. Questions will be answered with one of the following:

Contestants will not be involved in or exposed to discussion regarding their questions. However, in cases where the Scientific Committee feels that the contestant does not understand the task statement, English text which helps clarify the task may be added to the response, and if necessary, translated by the contestant's Delegation Leader into the language in which the question was originally posed.


In case the SC makes verbal announcements during the competition, these announcements will also be available on the Competition Server's web interface. The web interface also shows the current date of the CEOI's official clock, every time the page is loaded.

Competition Server

The CEOI competition takes place in a distributed environment in which each competitor has his or her own workstation for development and initial testing. Grading and evaluation take place on the Competition Server, which provides a similar execution environment to that of the contestant workstation.
Each competitor's workstation has only Linux installed. A set of software development tools will be available. These tools are used to develop solutions to the competition tasks. There is no restriction on the number of times a program may be edited, compiled, and run on the workstation.
The workstations will have network access to the Competition Server, to a web server which provides documentation, to relevant task data, and facilities such as printing, test execution, and solution submission.
The workstations will neither have access to each other nor the Internet. Any attempt to access another competitor's computer or the Internet will be considered cheating. Attempts to tamper with the Competition server, such as probing the server with customized URL's, will also be considered cheating.


Contestants are allowed to print only text files during the competition. After a contestant requests that a document be printed, the support staff will deliver the printout to the contestant; contestants should not leave their computer to find printouts. Printouts will be delivered as quickly as possible, but large volumes can produce delays in delivery. The submitted document will be formatted using a2ps (two pages per sheet). The limit on the length of the printout are 5 sheets. If a document to be printed is longer, it will be rejected. On each competition day the contestant can print at most 10 documents.

SUBMIT Interface

Contestants submit solutions to the Competition Server via a web browser.
When submitting their solution, contestants have to choose the task. The contest system determines the programming language by the file's suffix, see below.
Solutions for tasks may be submitted at any time.
For tasks which require output files as solutions, contestants must submit a zip file containing all output files. An explanation will be given in the task's description. The submission facility will validate the format of the submitted file, accepting only valid output files for grading.
For tasks that require programs as solutions, the submission facility will accept C, C++ or Pascal programs, verify that the program compiles and obeys the stated limits on program source size and compile time; the submission facility will then run the program on the sample test cases given in the task description, enforcing the relevant run-time resource constraints.
If the submitted program fails of one of these checks (i.e. output format check for output only tasks, sample testcases for batch and library tasks), the submission is not accepted for grading. This behaviour can be overridden when submitting by checking the box "accept, even if public testcases fail". This option should be used with care. The submission's status will be reported back to the contestant by the Contest Server as soon as possible.
For each task, the last accepted submission for that task will be used to award points.
Each submitted source program must be smaller than 1 MB and the evaluation server must be able to compile it in less than 30 seconds. Submitted programs which do not meet these constraints will be rejected by the submission system and the contestant will be notified. There is a limit of 50 submissions per task.

TEST Interface

The Competition Server runs Linux, enforces memory and time limits, presents input data to the contestant's program, and captures the results. For tasks that require programs as solutions a contestant may run his or her active submission in the evaluation environment using the TEST interface. To use this facility, the contestant supplies an input file to the interface. The TEST interface will execute the program, enforcing the resource limitations for the particular task. The screen output, the contents of the output file, execution time, and any applicable error messages will be displayed. The correctness of the output will not be verified, this is just a check whether the program can terminate with exit code 0 on the given input under the restrictions of the execution environment.
The TEST interface allows the contestant to determine the exact behavior of his or her program in the evaluation environment with respect to compilation parameters, time and memory limits, and so on.
Submitted input files must not exceed 10MB, every contestant is allowed to use the TEST interface at most 30 times per day. The test execution system will execute the program under Linux, enforcing the resource limitations for the particular task. The standard output, execution time, and any applicable error messages will be displayed.


Contestants may ask the support staff for assistance at any time. The staff members will not answer questions about the competition tasks, but will deliver Clarification Request Forms and printouts, help locate toilets and refreshments, and assist with computer and network problems. The only manner in which contestants are allowed to access the network is via web browser access to the designated Competition Server; even running a single 'ping' command is strictly prohibited. Contestants should never attempt to "fix" or "debug" or even "check" computer or network problems themselves; instead, they should ask for assistance.

Ending the Competition

Three warnings will be given at 15 minutes, 5 minutes, and 1 minute before the end of the round. Each warning will be given by an audible signal. The end of the round will be announced both verbally and by an audible signal. At the announcement ending the round, contestants must immediately stop working and wait at their desks without operating the computers or touching anything on their desks. An additional announcement will be made instructing them to leave their tables and exit the competition room.
At the end of the first competition round, any previously submitted items a contestant would like to use during the second competition round should be left at the workstation. All other items should be taken out of the competition hall, including task statements. At the end of the second competition round, contestants should remove all items including their mascots and dictionaries or any other previously submitted item; nothing should be left behind.


For output-only tasks, output files will be submitted one by one as a .zip file, explanations will be given on the task overview sheet, and scored as described in the task description.

For tasks that require programs as solutions, the submitted source files will be compiled under Linux, enforcing the source file size and compilation time constraints. The following commands will be used to compile solutions of tasks:

Language Suffix Compiler and Version Compilation command
C .c gcc >= 4.1 gcc -std=c99 -O2 -static -lm -DCONTEST
C++ .pas.cpp gcc >= 4.1 g++ -std=c++98 -O2 -static -lm -DCONTEST
Pascal .pas FreePascal >= 2.2 ppc386 -Mtp -Sg -O2 -XS -dCONTEST

Test run (batch and reactive tasks)

If the submitted solution compiled correctly, the grading system will, at some time later, execute the compiled program under Linux, enforcing the task-specific run-time and memory resource constraints with several inputs.
A test run refers to each time the solution is executed with a different input. For each test run the resource constraints will be enforced. If a program exceeds its allotment of any resource, the program is terminated and the test run is marked incorrect, without regard to any output produced.
If the program produces an output within the specified resource constraints, the output will be checked to verify its correctness. A score will be assigned to that specific test run depending on the output. Different test runs may have different maximum scores assigned to them.
If the test run is marked incorrect because it exceeded the resource constraints or because it produced an incorrect output it will be assigned a score of zero points.
For some tasks, partial credit may be awarded in a test run. Whenever this is possible it will be stated explicitly in the task description.
Upon termination, programs must always explicitly return an exit code 0. Other exit codes will be interpreted by the grading system as failures and no points will be awarded for the test run.

Test case

A test case is a set of one or more test runs. The score for a test case is defined as the minimum of the scores of its constituent test runs.
The purpose of a test case is to assess a well-defined characteristic of a program in a reliable and robust way. Such a characteristic could focus on, for instance, efficiency or special corner cases.
For every task there will be at least one "easy" test case, whose requirements will be separately stated in the task description.


The final score for any task will be obtained by adding the scores of each of the test cases for that task.
Only work which has been submitted to and accepted by the grading system will be awarded points.


Submitted programs are not allowed to:

All of the above actions are considered cheating, and may result in disqualification.

Appeal Process

Submitted solutions are judged using data which conforms to the specification given in the problem statement, but which is unknown to competitors during the competition.
Provisional grades, based on these tests, are handed out to team leaders as soon as they are available, shortly after competition ends. The judge data are made available electronically from the Contest Server. Contestants and team leaders may use the translation workstations to verify that the grades are assessed correctly.
A Team Leader may file an appeal by completing an Appeal Form and submitting the completed form to the SC until the GA meeting in the evening of the same day. Every appeal will be reviewed by the Scientific Committee and the team leader will be notified the committee's decision. All appeals and their disposition will be summarized at the final GA meeting of that competition day.
In the event that a mistake is discovered in the grading of a task, every successful submission of that task will be re-graded and re-scored whether or not the scoring of that submission has been appealed. Note that re-scoring may result in a higher or lower score for any contestant. Should anyone's score change after grading results have been distributed, new results will be printed and distributed to them.

Code of Conduct

Any contestant

will be considered to be cheating and is subject to disqualification. Also refer to the list above of prohibited program actions which are considered cheating and may result in disqualification.
Cheating will be taken very seriously and rules will be strictly enforced. Any contestant who is cheating in any way will be immediately disqualified, at the discretion of the International Scientific Committee. It is of the utmost importance that team leaders speak to their contestants about cheating, instructing and urging all contestants not to cheat, explaining the relevant rules and verifying that all contestants fully understand them.