PHP Dev Tools (for CodinGame or elsewhere)

Running your code locally (php)

Why?

So, if CodinGame provides everything, including a runtime environment, why do we need at all to be able to run your code locally?

Well, in 95% of the cases we just don't. But it can make sense when:

• If you have a non-obvious bug, it is much easier to debug it in the IDE, using breakpoints, line-by-line execution, variable inspection, etc. (More details in a later chapter.)
• If you have timeout in a CG puzzle, you might want to know how 'far' are you from passing. So run it locally without the time constraint, measure the running time with hrtime(), and print it to the console.
• For some optim puzzles you can pre-calculate some validator results locally without the time constraint, then hard-code it. It means that in the submitted code you just detect the input and send the correct output you already stored in your source as some string. Not a nice thing, feels a bit like a hack. I tried out this approach only in the 2048 puzzle.
• To improve your bot in bot programming games or contests, you can set up local self-play to try out new things without submitting to the arena. I used this approach to fine-tune some hyper-parameters ('magic constants' for an evaluation function) in my code.

Installing PHP

Depending on your OS, php might come already preinstalled, although it might be an older release. Try it out with php --version. While at the time of this writing CodinGame shamefully supports only v7.3 (released in 2018...), for your local environment you should go for the latest stable release (v8.1 till end of 2022).

• If using Ubuntu 20.04 LTS (directly or with Windows Subsystem for Linux (WSL)), it came with php v7.4 only, so there you needed to add an extra PPA repository to upgrade. However, Ubuntu 22.04 LTS already contains php v8.1, so it is best to upgrade the whole OS. Other Linux distros might have different status regarding php versions.

• For Windows you can download and unzip the latest release from the core php site.

  • You shall add its directory to the PATH, so you can run php from anywhere.
  • Copy the provided sample settings file php-development.ini to php.ini. There are lot of settings there, but 99% is just fine how it is.
  • The extension libraries are disabled by default. In php.ini look for the section with the ;extension= lines and remove the trailing ; to enable what you need. Most of the extensions you would need only for web applications, but not for CG puzzles. Some CG puzzles might need mbstring. Some other useful libraries such as bcmath and ctype are now part of the core, so always available (at least if compiled into php, but that is the case with the Windows distribution we downloaded).
  • The default memory setting is too low for some puzzles, increase it with memory_limit = 768M to match the CG environment, or you can even set it to unlimited with memory_limit = -1.

• You might find it more convenient to use a pre-packaged version. I use XAMPP that contains some additional useful stuff, such as a web server and a database besides PHP itself. (These are not needed for CodinGame puzzles though.) There are other similar packages as well.

  • You might still need to tweak php.ini settings to your liking.

• Mac users: I have no experience with it, so just google it...

• Using Docker containers is also possible, but setting up docker is beyond our scope, and I think it is a bit overkill for just solving some CG puzzles.

Optional: enabling JIT

In the default php config file the JIT compiler (available from v8.0) is turned off. While not a huge boost for typical web applications, for a computing-intensive CG puzzle the speedup is usually substantial: in my experience 2x to 3x.

To enable JIT, just uncomment / add / modify the following lines in your php.ini file:

zend_extension=opcache
opcache.enable = 1
opcache.enable_cli = 1
opcache.jit_buffer_size = 256M
opcache.jit = tracing

You can check if JIT is working by running:

php -r "var_dump(opcache_get_status()['jit']);"

Running a puzzle solution locally

While solo puzzle test cases are handled automaticaly on the CG site, locally we have to set up the input manually (as we do not want to type them at every run). In case of a solo puzzle, just select a testcase and copy-paste the input into a local file:

After saving the input to input_01.txt, run the test case with:

php my_solution.php < input_01.txt > output_01.txt 2>&1

...and check the result (what your code wrote to the standard output) in output_01.txt.

• Note: By adding 2>&1 above, we redirected the error log also to the same file.

• Beware: When creating a local test case input file, make sure to save it with Linux line ending LF instead of the Windows default CRLF, otherwise the input parsing might not work correctly.

• To run multiple test cases after each other, you can make a small batch file or shell script by copying and editing the above command line with different filenames.

Useful links

• PHP.net, the core language site (language documentation, releases, etc).
• XAMPP, a pre-packaged php distro for Windows, Max or Linux (includes Apache httpd, MariaDB, PHP, Perl, Tomcat, phpMyAdmin)

Coming next

Okay, we run our php code locally. But where shall we store our code?