Language: Python 2


General information

This tutorial gives a brief introduction to the evaluation platform and how to interact with it. It shows you how to solve a simple problem. The tutorial assumes that you are familiar with the choosen programming language.

When taking the test, you will be given a number of programming problems to solve. Each problem has a difficulty rating. The problems can be solved in any order; however, we suggest you start with the easiest. You will need to write a program to solve each of the problems. Feel free to use your preferred IDE, or our online text editor. Once you have created and tested the code, you will be able to submit your code for evaluation.

After you submit the code, it will be automatically evaluated. After some careful deliberation, you will get a judgement informing you whether your code behaved as expected or not. Look at How judging is done in the help for details on the judgement process and possible judgements returned from the system.

If the judgement is Accepted, your solution is deemed correct and sufficiently fast. You may submit additional attempts at the same problem, for example after cleaning up and commenting the code, or move on to the next problem. If the judgement is not accepted, you may debug your solution (with the judgement as a general guideline) and submit an alternate solution.

You can submit as many solutions as the allotted time allows. The last solution submitted for each problem will be used in assessing your programming proficiency.

Input/Output

Your program should read its input from standard input and produce output on standard output. This can for instance be done using sys.stdin / sys.stdout. Anything written on standard error (sys.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 Python 2, we use PyPy version Python 2.7.13 (7.3.1+dfsg-2, Apr 21 2020, 05:05:41) with the following flags: {files}.

System libraries

You are allowed to use all standard libraries included with Python 2.

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.

  1. The problem
  2. Reading the input
  3. Computing the answer
  4. The solution

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, there is a 64 bit integer type in Python 2, int.

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 sys.stdin, this can be done as below:

for line in sys.stdin: ab = line.split() a = int(ab[0]) b = int(ab[1]) # Solve the test case and output the answer

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) ≤ ab ≤ 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 print (assuming the int variable res holds the result):

print res

Step 4: The solution

Now we are basically done, all that remains is to combine the above parts.

Here is a version of the complete solution.

different.py


Frequently asked questions

Judging

I keep getting rejected but my solution works on the provided cases

The sample data provided in the problem statement is just there to help you make sure you understood what the problem asks for, and the input/output format. When you submit your solution, we will run it on an extensive set of additional test data to verify that it solves the problem correctly and efficiently.

When we run your solution, the first case(s) are always the sample case(s). If you fail on these, make sure that:

  1. You are not printing any output other than the one specified in the problem.
  2. You have not misspelled any part of the output (copy-paste is your friend).
  3. You are printing real-valued numbers with the precision requested in the problem.
If this does not help you get past the sample cases, make sure that there isn't a difference in system and compiler that causes your solution to behave differently when run on the judge machine.

I keep failing on testcase X. Can you please share it with me?

Sorry, no. We can't share the secret testdata.

There is an error in the sample data of the problem, can you please fix it?

The sample data is used to illustrate and clarify the problem. If you believe there is an error in the sample data, your interpretation of the problem is probably wrong. Consider if there is an alternative interpretation which matches the sample data.

How does judging work, and what do the different judgements mean, precisely?

See the judgements page.

Interacting with the judge system

Can I test my solution before I submit?

No, however we allow you to submit your solution multiple times so you can test your way to the right solution.

Do you store my submissions?

Yes, we store your submissions. Occasionally a problem is found with one of the problems (no pun intended) or a time limit is changed (this should not happen frequently) and then we need to rejudge all submissions on that problem. We also use the code to check for plagiarism.

I found a bug? / I have a question that is not answered in the documentation. / I think this or that would be much better if it worked like this instead.

Please tell us about it.

Python 2-specific questions

What implementation of python are you using?

We are currently using pypy to run your python programs. Pypy is considerably faster than CPython on most programs, but has a limited module support. For a list of technical differences see the PYPY documentation.

What python modules are available?

The base set of modules from Python are available. Note that specifically Scipy and Numpy are not possible to use.


External documentation

  1. Python 2