First steps

rbx (short for robox for setters) is the CLI tool robox provides for setters to prepare contests and problems.

You can start creating a new problem from a pre-initialized template by running rbx create [name].

rbx create test# This will create a `test` directory under the current# working directory with a pre-initialized problem template.

This is how the directory structure of the pre-initialized problem template will look like:

test
├── sols  # (1)!
│   ├── main.cpp
│   ├── slow.cpp
│   └── wa.cpp
├── statement  # (2)!
│   ├── olymp.sty
│   ├── projecao.png
│   ├── statement.rbx.tex
│   └── template.rbx.tex
├── tests  # (3)!
│   └── samples
│       ├── 000.in
│       └── 001.in
├── gen.cpp # (4)!
├── problem.rbx.yml # (5)!
├── random.txt # (6)!
├── random.py # (7)!
├── validator.cpp # (8)!
└── wcmp.cpp # (9)!

1. All solutions for the problem: the correct and the incorrect ones.
2. All statement-related assets, including the legend of the problem itself but also the tex templates and imported graphics.

3. Manually defined tests of the problem.

   Note

   Automatically generated tests are not defined by explicit input and output files, but are rather defined by generator entries in the problem configuration.

4. An example of a testlib generator. In this case, the generator is used to generate testcases for two testgroups: random and program-random.

   Note

   A problem can have multiple generators. This one is just an example.

5. The YAML configuration file for this problem.

6. A generator script for the problem.

   Each line of a generator script describes one call to a generator, and a generator script groups all these calls together.

   Example:

   gen 123
   gen 456
   

   Calls the generator named gen (here in this problem, implemented through gen.cpp) twice, thus generating two testcases.

   In this problem, this script is used to generate the testcase group random.

7. A program that outputs a generator script. Pretty similar to random.txt above, except that this is a program that prints to the stdout a generator script, and thus provides more flexibility to the setter.

   Example:

   #! /usr/bin/python3
   for i in range(10):
       print(f'gen {i}')
   

   This program outputs a generator script that creates 10 testcases with increasing parameter i.

   In this problem, this program is used to generate the testcase group program-random.

8. A testlib validator that checks whether the generated tests are in the correct format.

9. A built-in testlib checker that compares tokens of the participant's output and the judge's output.

Build

Let's skip the configuration of the problem for a second, and just build and run it. You can build a problem with rbx build. This will populate a build folder inside your problem's folder with all the testcases generated for the problem.

$ rbx build
$ ls build
build
│   └── tests
│       ├── program-random
│       │   └── ...
│       ├── random
│       │   └── ...
│       └── samples
│           └── ...

You can notice it created several folders inside a tests directory, each of which contains the tests for a specific testgroup. For this template in particular, we have three testsets: random, program-random and samples. We'll go into more details about each one of these in a minute.

Run

Now, let's execute rbx run. This command builds all testcases and executes each solution against them, evaluating whether each solution had the expected outcome.

$ rbx run

You can see this command prints a full run report: it shows for each testcase of each testgroup whether a certain solution passed or not. There are also links for the outputs of each problem.

Tip

You can notice when you called rbx run, the testcases were built really fast. That's because robox caches certain calls based on the hash tree of your package (similar to Makefile). You can explicitly clear this cache by calling rbx clean.

Result of the `rbx run` command.

Modifying the package

As you can see from the solutions and the statement, the pre-initialized template simply implements a problem where you have to add up two numbers A and B. Let's modify the problem to compute the sum of N numbers.

Rewrite solutions

Let's start rewriting the solutions. We can probably drop the slow solution since we're just naively summing numbers anyway.

We can develop the following accepted and wrong answer solutions.

sols/main.cppsols/wa.cpp

#include <bits/stdc++.h>

int32_t main() {
    int n;
    cin >> n;

    int64_t ans = 0;
    for(int i = 0; i < n; i++) {
        int x;
        cin >> x;
        ans += x;
    }

    cout << ans << endl;
}

#include <bits/stdc++.h>

int32_t main() {
    int n;
    cin >> n;

    int32_t ans = 0; // int32 overflows!!
    for(int i = 0; i < n; i++) {
        int x;
        cin >> x;
        ans += x;
    }

    cout << ans << endl;
}

To delete the slow.cpp solution from our package, we can just delete the file and the reference to it in problem.rbx.yml. The reference is located in the solutions section, which will look like this after the deletion:

solutions:
  - path: 'sols/main.cpp'
    outcome: ACCEPTED
  - path: 'sols/wa.cpp'
    outcome: WRONG_ANSWER

You can find the full list of expected outcomes here.

Write the validator

The testlib validator is implemented by validator.cpp and will look like this:

validator.cpp

#include "testlib.h"

using namespace std;

int main(int argc, char *argv[]) {
    registerValidation(argc, argv);
    prepareOpts(argc, argv);

    int MAX_N = opt<int>("MAX_N"); // (1)!

    for (int i = 0; i < n; i++) {
        if (i) inf.readSpace();
        inf.readInt(1, MAX_N, "A_i");
    }
    inf.readEoln();
    inf.readEof();
}

1. MAX_N is a variable defined in problem.rbx.yaml that is accessible in the validator. It allows you to change the constraints of the problem, and instantly replicate the change in validators and statements.

Generating random testcases

Now, let's rewrite our random generator to generate N numbers instead of only two.

We have to actually call this generator and generate testcases into some of the testgroups.

Let's delete the existing test groups in problem.rbx.yml, except for the samples one, and create a new main_tests group. Let's generate 10 random tests for this group by using a generator script. We can end up with the following files:

gen.cpprandom.pyproblem.rbx.yml

#include "testlib.h"

using namespace std;

int main(int argc, char *argv[]) {
    registerGen(argc, argv, 1); // (1)!

    int n = rnd.next(1, opt<int>(1));

    for (int i = 0; i < n; i++) {
        if (i) cout << " ";
        cout << rnd.next(1, opt<int>(2));
    }
    cout << endl;
}

1. The generator now receive two parameters MAX_N (accessed through opt<int>(1)) and MAX_A (accessed through opt<int>(2)).

for i in range(10):
    print(f'gen 1000 1000000000 {i}') # (1)!

1. This line defines 10 random calls to the generator gen, which will in turn generate testcases with N randomly varying from 1 to 1000 and the numbers to be added varying from 1 to 1e9.

   Tip

   Notice the trailing {i} being printed in every generator script line. That's because testlib rng seed is initialized from the argv given to the generator.

   Thus generators are reproducible: if we called gen 1000 10 times, we would always get the same result. By appending an extra variable {i}, we introduce randomness to the tests.

# Testcases section would look like:

testcases:
- name: 'samples'
    testcaseGlob: 'tests/samples/*.in'
- name: 'main_tests'  # (1)!
    generatorScript:
        path: 'random.py'

1. Here, main_tests would contain the 10 tests defined in random.py.

Now, if we run rbx build, we'd get our brand new generated tests.

Update the statement

Of course, last but not least, we have to update the statement of our problem. robox has its own statement format, called roboxTeX.

In statement/statement.rbx.tex you will find something like the following:

statement/statement.rbx.tex

%- block legend
Dado dois números inteiros $A$ e $B$, determine o valor de $A + B$.

\includegraphics[width=6cm]{projecao.png}
%- endblock

%- block input
A entrada é composta por uma única linha contendo dois números
inteiros $A$ e $B$ ($1 \leq A, B \leq \VAR{vars.MAX_N | sci}$). % (1)!
%- endblock

%- block output
A saída deve conter somente um único inteiro, a soma de $A$ e $B$.
%- endblock

%- block notes
Sem muitas notas pra este problema.
%- endblock

1. Notice the use of \VAR here, which is a command roboxTeX exposes for you to access variables defined in problem.rbx.yml, similar to how you accessed these in the testlib validator.

   The template engine used to expand \VAR{...} is Jinja2. This means we can also use filters. Here in particular, we're using a pre-defined filter implemented by roboxTeX called sci. This filter converts numbers with lots of zeroes (for instance, 100000), into their scientific notations (10^5).

As you can see, similar to Polygon, you write a few blocks of LaTeX that are expanded into a template. Here, the % delimits those pre-defined blocks. Your statement needs at least a legend, an input and an output.

Let's change each corresponding block to match our new problem description.

statement/statement.rbx.tex

%- block legend
Given $N$ integers, print their sum.
%- endblock

%- block input
The input has a single line containing $N$ 
($1 \leq N \leq \VAR{vars.MAX_N | sci}$) numbers. 
These numbers range from 1 to $\VAR{vars.MAX_A | sci}$.
%- endblock

%- block output
Print the sum of the integers.
%- endblock

%- block notes
No notes.
%- endblock

Advanced configuration

If you want to do more advanced changes to the package, you can continue reading our Reference section on the sidebar.

Package the problem

To build you problem, you can use the rbx package [platform] command.

Here, we'll build a Polygon package with our statement, and as such we'll need LaTeX dependencies installed to compile it to a PDF. You can read more about a few recommendations we have to install pdfLaTeX and other common dependencies here.

Note

Packages usually require a statement to be built.

You can try running rbx package [platform] --no-statement, but an error might be raised in case such platform does not support packages without statements.

$ rbx package polygon

A Polygon package will be built. This package can be directly uploaded to the Codeforces Gym through FTP.