Problem_Format.mw

This is a draft. Sections <s>highlighted in yellow</s> have not been implemented in the reference implementation of the problem format tool chain. This might imply that that part of the specification is more in flux. Sections <s class="dep">highlighted in red</s> are deprecated.

== Overview ==

This document describes the format of a ''Kattis problem package'', used for distributing and sharing problems for algorithmic programming contests as well as educational use. 

=== General Requirements ===

The package consists of a single directory containing files as described below, or alternatively, a ZIP compressed archive of the same files using the file extension <tt>.kpp</tt> . The name of the directory or the base name of the archive must consisting solely of lower case letters a-z and digits 0-9.  

All file names for files included in the package must match the following regexp

 [a-zA-Z0-9][a-zA-Z0-9_.-]*[a-zA-Z0-9]

I.e., it must be of length at least 2, consist solely of lower or upper case letters a-z, A-Z, digits 0-9, period, dash or underscore, but must not begin or end with period, dash or underscore. 

All text files for a problem must be UTF-8 encoded and not have a byte order mark.

All floating point numbers must be given as the external character sequences defined by IEEE 754-2008 and may use up to double precision.

=== Programs ===

There are a number of different kinds of programs that may be provided in the problem package; submissions, input validators, output validators, graders and generators. All programs are always represented by a single file or directory. In other words, if a program consists of several files, these must be provided in a single directory. The name of the program, for the purpose of referring to it within the package is the base name of the file or the name of the directory. There can't be two programs of the same kind with the same name.

Validators and graders, but not submissions, in the form of a directory may include two POSIX-compliant scripts "build" and "run". Either both or none of these scripts must be included.
If the scripts are present, then:
* the program will be compiled by executing the build script.
* the program will be run by executing the run script.

Programs without build and run scripts are built and run according to what language is used. Language is determined by looking at the file endings. If a single language from the table below can't be determined, building fails. In the case of Python 2 and 3 which share the same file ending, language will be determined by looking at the shebang line which must match the regular expressions in the table below.

For languages where there could be several entry points, the default entry point in the table below will be used. 

{| class="wikitable"
! Code !! Language !! Default entry point !! File endings !! Shebang
|-
| c || C || || .c ||
|-
| cpp || C++ || || .cc, .cpp, .cxx, .c++, .C ||
|-
| csharp || C# || || .cs ||
|-
| go || Go || || .go ||
|-
| haskell || Haskell || || .hs ||
|-
| java || Java || Main || .java ||
|-
| javascript || JavaScript || main.js  || .js ||
|-
| kotlin || Kotlin || MainKt || .kt ||
|-
| lisp || Common Lisp || main.{lisp,cl} || .lisp .cl ||
|-
| objectivec || Objective-C || || .m ||
|-
| ocaml || OCaml || || *.ml ||
|-
| pascal || Pascal || || .pas ||
|-
| php || PHP || main.php || .php ||
|-
| prolog || Prolog || || .pl ||
|-
| python2 || Python 2 || main.py || .py || Matches the regex "<tt>^#!.*python2 </tt>", and default if shebang does not match any other language
|-
| python3 || Python 3 || main.py || .py || Matches the regex "<tt>^#!.*python3 </tt>"
|-
| ruby || Ruby || || .rb ||
|-
| rust || Rust || || .rs ||
|-
| scala || Scala || || .scala ||
|}

=== Problem types ===

There are two types of problems: <em>pass-fail</em> problems and <em>scoring</em> problems.  In pass-fail problems, submissions are basically judged as either accepted or rejected (though the "rejected" judgement is more fine-grained and divided into results such as "Wrong Answer", "Time Limit Exceeded", etc).  In scoring problems, a submission that is accepted is additionally given a score, which is a numeric value (and the goal is to either maximize or minimize this value).

== Problem Metadata ==

Metadata about the problem (e.g., source, license, limits) are provided in a UTF-8 encoded YAML file named <tt>problem.yaml</tt> placed in the root directory of the package.  

The keys are defined as below. Keys are optional unless explicitly stated. Any unknown keys should be treated as an error.

{| class="wikitable"
! Key !! Type !! Default !! Comments
|-
| <s>name</s> || <s>String or map of strings</s> || || <s>Required. If a string this is the name of the problem in english. If a map the keys are language codes and the values are the name of the problem in that language. It is an error for a language to be missing if there exists a problem statement for that language.</s>
|-
| type || String || pass-fail || One of "pass-fail" and "scoring".
|-
| author || String ||  || Who should get author credits. This would typically be the people that came up with the idea, wrote the problem specification and created the test data. This is sometimes omitted when authors choose to instead only give source credit, but both may be specified.
|-
| source || String ||  || Who should get source credit. This would typically be the name (and year) of the event where the problem was first used or created for.
|-
| source_url || String || || Link to page for source event. Must not be given if source is not.
|-
| license || String || unknown || License under which the problem may be used. Value has to be one of the ones defined below.
|-
| rights_owner || String || Value of author, if present, otherwise value of source. || Owner of the copyright of the problem. If not present, author is owner. If author is not present either, source is owner. Required if license is something other than "unknown" or "public domain". Forbidden if license is "public domain".
|-
| limits || Map with keys as defined below || see definition below ||
|-
| validation || String || default || One of "default" or "custom".  If "custom", may be followed by some subset of "score" and "interactive", where "score" indicates that the validator produces a score (this is only valid for scoring problems), and "interactive" specifies that the validator is run interactively with a submission.  For example, "custom interactive score". 
|-
| validator_flags || String || || Will be passed as command-line arguments to each of the output validators.
|-
| <s class="dep">grading</s> <s>scoring</s> || Map with keys as defined below || See definition below ||  Must only be used on scoring problems.
|-
| keywords || <s>String or sequence of strings</s> || || Set of keywords.
|-
| <s>uuid</s> || <s>String</s> || || <s>UUID identifying the problem.</s>
|-
| <s>libraries</s> || <s>String or sequence of strings</s> || || <s>Set of libraries as defined below.</s>
|-
| <s>languages</s> || <s>String or sequence of strings</s> || <s>all</s> || <s>Set of languages or "all".</s>
|}

=== license ===

Allowed values for license.

Values other than ''unknown'' or ''public domain'' requires rights_owner to have a value.

{| class="wikitable"
! Value !! Comments !! Link
|-
| unknown || The default value. In practice means that the problem can not be used. ||
|-
| public domain || There are no known copyrights on the problem, anywhere in the world. || http://creativecommons.org/about/pdm
|-
| cc0 || CC0, "no rights reserved" || http://creativecommons.org/about/cc0
|-
| cc by || CC attribution || http://creativecommons.org/licenses/by/3.0/
|-
| cc by-sa || CC attribution, share alike || http://creativecommons.org/licenses/by-sa/3.0/
|-
| educational || May be freely used for educational purposes ||
|-
| permission || Used with permission. The author must be contacted for every additional use. ||
|}

=== limits ===

A map with the following keys:

{| class="wikitable"
! Key !! Comments !! Default !! Typical system default
|-
| time_multiplier || optional || 5 ||
|-
| time_safety_margin || optional || 2 ||
|-
| memory || optional, in MiB || system default || 2048
|-
| output || optional, in MiB || system default || 8 
|-
| code || optional, in kiB	|| system default || 128
|-
| compilation_time || optional, in seconds || system default || 60
|-
| compilation_memory || optional, in MiB || system default || 2048
|-
| validation_time || optional, in seconds || system default || 60
|-
| validation_memory || optional, in MiB || system default || 2048
|-
| validation_output || optional, in MiB || system default || 8 
|}

For most keys the system default will be used if nothing is specified. This can vary, but you SHOULD assume that it's reasonable. Only specify limits when the problem needs a specific limit, but do specify limits even if the "typical system default" is what is needed.

=== <s class="dep">grading</s> <s>scoring</s> ===

A map with the following keys:

{| class="wikitable"
! Key !! Type !! Default !! Comments
|-
| objective || String || max || One of "min" or "max" specifying whether it is a minimization or a maximization problem.
|-
| show_test_data_groups || boolean || false || Specifies whether test group results should be shown to the end user.
|-
|}

=== libraries ===
<s>
A set from elements below. A library will be available for the languages listed.
</s>
{| class="wikitable"
! Value !! Library !! Languages
|-
| gmp || GMP - The GNU Multiple Precision Arithmetic Library || C, C++
|-
| boost || Boost || C++
|}

=== languages ===
<s>
A space separated list of language code from the table in the overview section or ''all''.

If a list is given, the problem may only be solved using those languages.
</s>

== Problem Statements ==

The problem statement of the problem is provided in the directory <tt>problem_statement/</tt>.

This directory must contain one file per language, for at least one language, named <tt>problem.<language>.<filetype></tt>, that contains the problem text itself, including input
and output specifications, but not sample input and output.  <s class='dep'>Language must be given as an ISO 639-1 alpha-2 language code.</s>  <s>Language must be given as the shortest ISO 639 code. If needed a hyphen and a ISO 3166-1 alpha-2 code may be appended to ISO 639 code.</s> Optionally, the language code can be left out, the default is then English (<tt>en</tt>). Filetype can be either <tt>tex</tt> for LaTeX files<s>, <tt>md</tt> for Markdown, or <tt>pdf</tt> for PDF</s>. 

Please note that many kinds of transformations on the problem statements, such as conversion to HTML or styling to fit in a single document containing many problems will not be possible for PDF problem statements, so using this format should be avoided if at all possible.

Auxiliary files needed by the problem statement files must all be in <tt><short_name>/problem_statement/</tt> , <tt>problem.<language>.<filetype></tt> should reference auxiliary files as if the
working directory is <tt><short_name>/problem_statement/</tt>. Image file formats supported are <tt>.png</tt>, <tt>.jpg</tt>, <tt>.jpeg</tt>, and <tt>.pdf</tt>.

A LaTeX file may include the Problem name using the LaTeX command <tt>\problemname</tt> in case LaTeX formatting of the title is wanted. <s>If it's not included the problem name specified in <tt>problem.yaml</tt> will be used.</s>

The problem statements must only contain the actual problem statement, no sample data.

== Attachments ==

Public, i.e. non-secret, files to be made available in addition to the problem statement and sample test data are provided in the directory <tt>attachments/</tt>.

== Test data ==

<s>
If input generators are used the files described here might not be available in this directory. This section describes what must be the case after running the generators.
</s>

The test data are provided in subdirectories of <tt>data/</tt>. The sample data in <tt>data/sample/</tt> and the secret data in <tt>data/secret/</tt>.

All input and answer files have the filename extension <tt>.in</tt> and <tt>.ans</tt> respectively. 

=== Annotations ===

Optionally a hint, a description and an illustration file may be provided.

The hint file is a text file with filename extension<tt>.hint</tt> giving a hint for solving an input file. The hint file is meant to be given as feedback, i.e. to somebody that fails to solve the problem. 

The description file is a text file with filename extension <tt>.desc</tt> describing the purpose of an input file. The description file is meant to be privileged information that explains the purpose of the related test file, e.g. what cases it's supposed to test.

The Illustration is an image file with filename extension <tt>.png</tt>, <tt>.jpg</tt>, <tt>.jpeg</tt>, or <tt>.svg</tt>. The illustration is meant to be privileged information illustrating the related test file.

Input, answer, description, hint and image files are matched by the base name.

=== Test Data Groups ===

The test data for the problem can be organized into a tree-like structure.  Each node of this tree is represented by a directory and referred to as a test data group.  Each test data group may consist of zero or more test cases (i.e., input-answer files) and zero or more subgroups of test data (i.e., subdirectories).

At the top level, the test data is divided into exactly two groups: <tt>sample</tt> and <tt>secret</tt>, but these two groups may be further split into subgroups as desired.

The <em>result</em> of a test data group is computed by applying a <em>grader</em> to all of the sub-results (test cases and subgroups) in the group.  See [[#Graders|Graders]] for more details.

Test files and groups will be used in lexicographical order on file base name. If a specific order is desired a numbered prefix such as 00, 01, 02, 03, and so on, can be used.

In each test data group, a file <tt>testdata.yaml</tt> may be placed to specify how the result of the test data group should be computed.  If such a file is not provided for a test data group then the settings for the parent group will be used.  The format of <tt>testdata.yaml</tt> is as follows:

{| class="wikitable"
! Key !! Type !! Default !! Comments
|-
| on_reject || String || break || One of "break" or "continue".  Specifies how judging should proceed when a submission gets a non-Accept judgement on an individual test file or subgroup.  If "break", judging proceeds immediately to grading.  If "continue", judging continues judging the rest of the test files and subgroups within the group.
|-
| grading || String || default || One of "default" and "custom".
|-
| grader_flags || String  || empty string|| arguments passed to the grader for this test data group.
|-
| input_validator<s class="dep">_flags</s> || String <s>or map with the keys "name" and "flags"</s> || empty string || <s class="dep">arguments passed to the input validator for this test data group.</s> <s>If a string this is the name of the input validator that will be used for this test data group. If a map then this is the name as well as the flags that will be passed to the input validator.</s>
|-
| output_validator<s class="dep">_flags</s> || String <s>or map with the keys "name" and "flags"</s> || empty string || <s class="dep">arguments passed to the output validator for this test data group.</s> <s>If a string this is the name of the output validator that will be used for this test data group. If a map then this is the name as well as the flags that will be passed to the output validator.</s>
|-
| accept_score || String || 1 || Default score for accepted input files.  May only be specified for scoring problems.
|-
| reject_score || String || 0 || Default score for rejected input files.  May only be specified for scoring problems.
|-
| range || String || -inf +inf || Two numbers A and B ("inf", "-inf", "+inf" are allowed for plus/minus infinity) specifying the range of possible scores.  May only be specified for scoring problems.
|}

== Included Code ==

Code that should be included with all submissions are provided in one directory per supported language, called <tt>include/<language>/</tt>. 

The files should be copied from a language directory based on the language of the submission, to the submission files before compiling, overwriting files from the submission in the case of name collision. Language must be given as one of the language codes in the language table in the overview section. If any of the included files are supposed to be the main file (i.e. a driver), that file must have the language dependent name as given in the table referred above.

== Example Submissions ==

Correct and incorrect solutions to the problem are provided in subdirectories of <tt>submissions/</tt>.  The possible subdirectories are:

{| class="wikitable"
! Value !! Requirement !! Comment
|-
| accepted || Accepted as a correct solution for all test files || At least one is required.
|-
| partially_accepted || Overall verdict must be Accepted. Overall score must not be max of range if objective is max and min of range if objective is min. || Must not be used for pass-fail problems.
|-
| wrong_answer || Wrong answer for some test file, but is not too slow and does not crash for any test file ||
|-
| time_limit_exceeded || Too slow for some test file. May also give wrong answer but not crash for any test file.  ||
|-
| run_time_error || Crashes for some test file ||
|}

<s>For submissions of type <tt>accepted</tt> and scoring problems, the expected score can be specified by including the string <tt>@EXPECTED_SCORE@:</tt> followed by the expected score somewhere in the source code, e.g. in a comment.</s>

Every file or directory in these directories represents a separate solution.  Same requirements as for submissions with regards to filenames. It is mandatory to provide at least one accepted solution. 

Submissions must read input data from standard input, and write output to standard output.

== Input Validators ==

Input Validators, for verifying the correctness of the input files, are provided in <s class="dep"><tt>input_format_validators/</tt></s> <s><tt>input_validators/</tt></s>.  Input validators can be specified as VIVA-files (with file ending <tt>.viva</tt>), Checktestdata-file (with file ending <tt>.ctd</tt>), or as a program.

All input validators provided will be run on every input file. Validation fails if any validator fails.

=== Invocation ===

An input validator program must be an application (executable or interpreted) capable of being invoked with a command line call. 

All input validators provided will be run on every test data file using the arguments specified for the test data group they are part of. Validation fails if any validator fails.

When invoked the input validator will get the input file on stdin.

The validator should be possible to use as follows on the command line:

  ./validator [arguments] < inputfile

=== Output ===

The input validator may output debug information on stdout and stderr. This information may be displayed to the user upon invocation of the validator.

=== Exit codes ===

The input validator must exit with code 42 on successful validation. Any other exit code means that the input file could not be confirmed as valid.

==== Dependencies ====

The validator MUST NOT read any files outside those defined in
the Invocation section. Its result MUST depend only on these
files and the arguments.

== Output Validators ==

Output Validators are used if the problem requires more complicated output validation than what is provided by the default diff variant described below.  They are provided in <tt>output_validators/</tt>, and must adhere to the [[Output validator]] specification.

All output validators provided will be run on the output for every test data file using the arguments specified for the test data group they are part of. Validation fails if any validator fails.

=== Default Output Validator Specification ===

The default output validator is essentially a beefed-up diff. In its default mode, it
tokenizes the files to compare and compares them token by token. It supports the
following command-line arguments to control how tokens are compared.

{| class="wikitable"
! Arguments !! Description
|-
| <tt>case_sensitive</tt> || indicates that comparisons should be case-sensitive.
|-
| <tt>space_change_sensitive</tt> || indicates that changes in the amount of whitespace should be rejected (the default is that any sequence of 1 or more
whitespace characters are equivalent).
|-
| <tt>float_relative_tolerance &epsilon;</tt> || indicates that floating-point tokens should be accepted if they are within relative error &le; &epsilon; (see below for details).
|-
| <tt>float_absolute_tolerance &epsilon;</tt> || indicates that floating-point tokens should be accepted if they are within absolute error &le; &epsilon; (see below for details).
|-
| <tt>float_tolerance &epsilon;</tt> || short-hand for applying &epsilon; as both relative and absolute tolerance.
|}

When supplying both a relative and an absolute tolerance, the semantics are that a token is accepted if it is within either of the two tolerances.
When a floating-point tolerance has been set, any valid formatting of floating point numbers is accepted for floating point tokens. So for instance if a token in the answer file says <tt>0.0314</tt>, a token of <tt>3.14000000e-2</tt> in the output file would be accepted. If no floating point tolerance has been set, floating point tokens are treated just like any other token and has to match exactly.

== Graders ==

Graders are programs that are given the sub-results of a test data group and aggregate a result for the group. They are provided in <tt>graders/</tt> .

For pass-fail problems, this grader will typically just set the verdict to accepted if all sub-results in the group were accepted and otherwise select the "worst" error in the group (see below for definition of "worst"), though it is possible to write a custom grader which e.g. accepts if at least half the sub-results are accepted.  For scoring problems, one common grader behaviour would be to always set the verdict to Accepted, with the score being the sum of scores of the items in the test group.

=== Invocation ===

A grader program must be an application (executable or interpreted) capable of being invoked with a command line call. 

When invoked the grader will get the judgement for test files or groups on stdin and is expected to produce an aggregate result on stdout.

The grader should be possible to use as follows on the command line:

 ./grader [arguments] < judgeresults

On success, the grader must exit with exit code 0.

=== Input ===

A grader simply takes a list of results on standard input, and produces a single result on standard output.  The input file will have the one line per test file containing the result of judging the testfile, using the code from the table below, followed by whitespace, followed by the score.  <s>Format to be extended.</s>

{| class="wikitable"
! Code !! Meaning
|-
| AC || Accepted
|-
| WA || Wrong Answer
|-
| RTE || Run-Time Error
|-
| TLE || Time-Limit Exceeded
|}

The score is taken from the <tt>score.txt</tt> files produced by the ouput validator. If no <tt>score.txt</tt> exists the score will be as defined by the grading accept_score and reject_score setting from problem.yaml.

=== Output ===

The grader must output the aggregate result on stdout in the same format as its input. Any other output, including no output, will result in a Judging Error.

For pass-fail problems, or for non-Accepted results on scoring problems, the score provided by the grader will always be ignored.

The grader may output debug information on stderr. This information may be displayed to the user upon invocation of the grader.

=== Default Grader Specification ===

The default grader has three different modes for aggregating the verdict -- ''worst_error'', ''first_error'' and ''always_accept'' -- four different modes for aggregating the score -- ''sum'', ''avg'', ''min'', ''max'' -- and two flags -- ''ignore_sample'' and ''accept_if_any_accepted''.  These modes can be set by providing their names as command line arguments (through the "grader_flags" option in [[#Test Data Groups|testdata.yaml]]).  If multiple conflicting modes are given, the last one is used.  Their meaning are as follows.

{| class="wikitable"
! Argument !! Type !! Description
|-
| <tt>worst_error</tt> <s class="dep"><tt>no_errors</tt></s> || verdict mode || Default.  Verdict is accepted if all subresults are accepted, otherwise it is the first of JE, IF, RTE, MLE, TLE, OLE, WA that is the subresult of some item in the test case group.  Note that in combination with the on_reject:break policy in testdata.yaml, the result will be the first error encountered.
|-
| <tt>first_error</tt> || verdict mode || Verdict is accepted if all subresults are accepted, otherwise it is the verdict of the first subresult with a non-accepted verdict. Please note <tt>worst_error</tt> and <tt>first_error</tt> always give the same result if <tt>on_reject</tt> is set to <tt>break</tt>, and as such it is recommended to use the default.
|-
| <tt>always_accept</tt> || verdict mode || Verdict is always accepted.
|-
| <tt>sum</tt> || scoring mode || Default.  Score is sum of input scores.
|-
| <tt>avg</tt> || scoring mode || score is average of input scores.
|-
| <tt>min</tt> || scoring mode || score is minimum of input scores.
|-
| <tt>max</tt> || scoring mode || score is maximum of input scores.
|-
| <tt>ignore_sample</tt> || flag || Must only be used on the root level. The first subresult (sample) will be ignored, the second subresult (secret) will be used, both verdict and score.
|-
| <tt>accept_if_any_accepted</tt> || flag || Verdict is accepted if any subresult is accepted, otherwise as specified by the verdict aggregation mode.
|}

== <s>Generators</s> ==
<s>
Input generators are programs that generates input. They are provided in <tt>generators/</tt>.
</s>
=== <s>Invocation</s> ===
<s>
A generator program must be an application (executable or interpreted) capable of being invoked with a command line call.

The generators will be run with the test data directory (<tt>data/</tt>) as the working directory. The generator may read any existing files in that directory and should create any kind of test data file as defined in the test data section. The generator may not read or write anything outside the test data directory. The generators will be run in lexicographical order on name. If a specific order is desired a numbered prefix such as 00, 01, 02, 03, and so on, can be used.

The generators must be deterministic, i.e. always produce the same input file when give the same arguments.

The generators must be idempotent, i.e. running them multiple times should result in the same contents of the test data directory as running them once.
</s>

== See also ==

* [[Output validator]]
* [[Sample problem.yaml]]
* [[Problem format directory structure]]
* [[Problem Format Verification]]