PHP
General information
You start out by finding a suitable problem to solve. Then you write code to solve the problem. After this, you submit the code to us for review. We will then compile your code and run it on some secret input. After some careful deliberation, you will get a judgement informing you whether your code behaved as expected or not.
Input/Output
Your program should read its input from standard input and produce output on standard output.
This can for instance be done using fscanf(STDIN, ...)
/ fprintf(STDOUT, ...)
.
Anything written on standard error fprintf(STDERR, ...)
will be ignored. This can be used for debugging your program during development (i.e., you do not have to remove debug output before submitting if you use standard error for debug output). Of course, writing to standard error will take some runtime.
Input will always follow the input specification (so you do not need to validate the input). Your output must follow the output specification.
Compiler settings
For PHP, we use php version PHP 8.1.2-1ubuntu2.14 (cli) (built: Aug 18 2023 11:41:11) (NTS) with the following flags: -n -d display_errors=stderr -d html_errors=0 -l {files}
.
Runtime settings
For PHP, we use php version PHP 8.1.2-1ubuntu2.14 (cli) (built: Aug 18 2023 11:41:11) (NTS) with the following runtime flags: -n -d display_errors=stderr -d html_errors=0 -d memory_limit={memlim}m -r "{php_preamble} require {mainfile};"
.
Here {memlim} is the actual memory limit for the problem you are submitting to.
File Extensions
Files with any of the following file extensions will be used: .php
System libraries
You are allowed to use all standard libraries included with PHP.
Hardware
We are currently using Dell PowerEdge R230 servers for judging. These are equipped with an Intel Xeon E3-1220V6 CPU running at 3.0 GHz and 8 GB RAM. A 64-bit Linux kernel is used.
Exiting
We will inspect the exit code of your program. If it is non-zero, we will judge your submission as Run Time Error.
Solving a problem
Now lets get down to business and write some code. The short tutorial below goes through the solution of A Different Problem.
Step 1: The problem
You are tasked with writing a program that computes the difference between integers. Sounds simple, doesn't it? Well, as we will see, the problem still holds some small difficulties.
Step 2: Reading the input
One thing to note is that the integers can be
fairly large, as large as 1015. Luckily,
our system is 64-bit and the php int
is large enough.
Now that we have determined a suitable type, we just
have to read the data. Reading is done from standard
input. In this problem, we should read until the end
of the file (in other problems, there might be an
integer at the beginning of the input, specifying how
much to read, or there might be a special indicator
denoting that there is nothing more to read). Using
fscanf()
, this can be done as below:
Step 3: Computing the answer
Now that we've read the input, it's time to actually
solve the problem. Since 0 ≤ a, b ≤
1015, we have that −(1015)
≤ a−b ≤ 1015,
which means that there is no danger of overflow
involved in just subtracting the two numbers
a and b. Then, we can
just take the absolute value by using the abs
function.
Finally, it's time to print the result. Using
fprintf()
(assuming the variable
$res
holds the result):
Step 4: The solution
Now we are basically done, all that remains is to combine the above parts.