Frequently Asked Questions

4 min read

Well, a lot of people seem to be having the same kind of questions across different forums and different problems. Here is a brief list of questions that have been coming up quite frequently over the past few weeks, and some hints on what you should do to solve the issue.

Q. What compilers do we use?
A. The compilers for the different languages are specified when you select the language while submitting the  solution. Code compiled on other non-standard compilers cannot be guaranteed to compile on the online judge system.

Q. What are the system specifications?
A. As of now, the specifications of the system on which the judge executes the solutions are :
Operating System : Gentoo Linux
Processor : Quad Core Intel running at 2.33 GHz
Memory : 4 GB of RAM (64 MB guaranteed for each submission)
Storage : 160 GB effective storage using SATA RAID 0 configuration
Network Link : 144 Mbit maximum throughput

Q. I can’t seem to find the compilers being used by Codechef. Can you give me a link?
A. The IDEs / Compilers / Interpreters for some commonly  used languages are listed below.
C / C++ : You can use the Dev C++ IDE if you are on windows – http://www.bloodshed.net/dev/devcpp.html
Java : Download the Java Development Kit from the Sun website – http://java.sun.com/javase/downloads/index.jsp
Python : Download the python interpreter from – http://www.python.org/download/
Perl : Download perl from http://www.perl.com/download.csp
Ruby : Download it from http://www.ruby-lang.org/en/downloads/
C# : Download it from http://www.microsoft.com/express/vcsharp/

You can use flags like -O2 in C or C++ to turn on compiler level optimization.

Q. Why does my code compile fine in Turbo C but not on the Codechef Judge?
A. The Codechef Judge uses the GNU compiler collection. Turbo C uses some non-standard headers and as such should not be used. A standards compliant C code written under Turbo C will compile fine on the online judge.

Q. Can I include the file conio.h?
A. No, conio.h is not a standard header file and as such is not available under the GNU compiler collection. Code which includes conio.h will not compile on the online judge.

Q. What should I name the class in a java solution?
A. You should name the class as Main. Failure to do so will result in a compilation error on the online judge system.

Q. Do I need to take the input for all testcases at once before processing it?

A. No, you need not take all the input at once. You can take the input for a particular test case and output the answer and then proceed to the next test case. Program should read from standard input and write into standard output. There is no need to read all data first, compute them all and then print all output. It is recommended to read and write data as simultaneously. Technically, server redirects standard stream to files. You can test you programs in the same way at home.

Q. Can I get the input for which my program failed?
A. Currently it is not possible to get the input for which your program fails. Thinking out corner cases is a part of the fun associated with algorithms 🙂

Q. How do I take input for problems which do not specify a distinct terminating condition or the number of test cases?
A. In cases where the total number of test cases are not specified or some input doesn’t serve as the terminating input, you are expected to take input till an EOF marker is encountered. While testing, you can terminate the input in the command line by pressing the <ctrl> and <z> keys together.

Q. How do I get the execution time of a program in Linux?
A. After compiling the program, say you have the output file with the name ‘solution’, then, you can get the execution time by using the command “time ./solution”. The sys and user times are what you should be looking at in the output.

Q. The code runs within the time limit on my system, but I get a TLE on Codechef. Why is that so?
A. TLE stands for Time Limit Exceeded. The configuration of your system might be different from the one we use. You need to optimize your algorithm or come up with a better algorithm.

Q. I can’t even take input or print output within the time limit, let alone processing the input. What should I do?
A. Make sure you have submitted an efficient solution to http://www.codechef.com/problems/INTEST/ and http://www.codechef.com/problems/TEST/ and make sure you read http://blog.codechef.com/2009/02/24/54/

Q. The time limit for the problem is 2 seconds, but some accepted solutions take more time. How is that possible?

A. This can happen if the problem has multiple test case files. The time mentioned in the constraints is per input file. If there are multiple input files, then the total time taken for executing all of them is displayed. For example, if the time constraint for the problem is 2 seconds and there are 8 input files, then your program must take at most 2 seconds for any particular input file, but the total time displayed will be the sum of the execution times for the 8 input files and this may exceed 2 seconds.

Q. Why do I get an error called SIGSEGV?
A. A SIGSEGV is an error(signal) caused by an invalid memory reference or a segmentation fault. You are probably trying to access an array element out of bounds or trying to use too much memory. Some of the other causes of a segmentation fault are : Using uninitialized pointers, dereference of NULL pointers, accessing memory that the program doesn’t own.

Q. Why do I get an error called SIGABRT?
A. A SIGABRT is caused if your program aborted due to a fatal error. This can also be caused if you are using an assert() which fails or an abort().

Q. Why do I get an error called SIGFPE?
A. A SIGFPE is caused by a floating point error. Your program is encountering such an error, probably a division by zero or some similar undefined operation.

Q. Why do I get an error called NZEC?
A. NZEC stands for Non Zero Exit Code. Usually, returning non-zero values from main() will cause this error. It helps telling crash from WA (Wrong Answer) with interpreted languages. Typically this would happen if you omit a return 0; from main() in C. For interpreted languages or Java/C++, this could happen if your program threw an exception which was not caught (e.g. Trying to allocate too much memory in a vector).

If you have any other questions, do post them as a comment and we will try to incorporate them into the FAQ.

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83 Replies to “Frequently Asked Questions”

    1. Currently only previous contest problem submissions are available as well as two easy practice problems. We will continue to make solutions to past contests available. Soon we will have a visual indicator showing which problems have solutions available.
      Cheers

    1. Currently only previous contest problem submissions are available as well as two easy practice problems. We will continue to make solutions to past contests available. Soon we will have a visual indicator showing which problems have solutions available.
      Cheers

  1. many programs submitted in codechef written in C/C++ include header file

    as far as i kno… there’s no such header file in Turbo C compiler ( the one i use)…. please mention which header file is it?

  2. many programs submitted in codechef written in C/C++ include header file

    as far as i kno… there’s no such header file in Turbo C compiler ( the one i use)…. please mention which header file is it?

  3. @nitin You might want to go through the sample programs in the help section on the site. http://www.codechef.com/help/

    @Frank No plans to do this at the moment. If something comes up, we will let you know.

    @Johnes You are probably having some issues with the way you are doing your IO. You might want to check that again.

  4. I am using Turbo c++ IDE …is there any way…i can use this compiler and avoid the runtime error (NZEC) that i am getting, everytime i submit a sulution…

  5. I am using Turbo c++ IDE …is there any way…i can use this compiler and avoid the runtime error (NZEC) that i am getting, everytime i submit a sulution…

  6. Hey people,

    Just now I submitted my first program in this site but it said “Compilation Failed” though it compiled fine in my system JDK1.6 . Even I was looking for JDK1.6 option in the drop down provided while submitting it but there was only JDK1.5. Now what should I do?

    Thanks !

  7. Hey people,

    Just now I submitted my first program in this site but it said “Compilation Failed” though it compiled fine in my system JDK1.6 . Even I was looking for JDK1.6 option in the drop down provided while submitting it but there was only JDK1.5. Now what should I do?

    Thanks !

  8. I had tested my program independently. It was working fine. I had tested for few scenarios including the sample input given in the CEO Ride problem. Only after successfully testing I had submitted it here. It is said that it was failed due to run time error. How can I get more info on this.

    Thanks
    Maheshwar

  9. I had tested my program independently. It was working fine. I had tested for few scenarios including the sample input given in the CEO Ride problem. Only after successfully testing I had submitted it here. It is said that it was failed due to run time error. How can I get more info on this.

    Thanks
    Maheshwar

  10. You can get a runtime error because of a variety of reasons. You can get a segfault if you are accessing memory which you are not supposed to. You can get a NZEC if your code does not exit with a return status of 0 etc. Depending on what the error code is, you can debug your code and try finding out what is going wrong and where.

  11. You can get a runtime error because of a variety of reasons. You can get a segfault if you are accessing memory which you are not supposed to. You can get a NZEC if your code does not exit with a return status of 0 etc. Depending on what the error code is, you can debug your code and try finding out what is going wrong and where.

  12. Some Language takes More time of execution then Others for eg compare java and c++ so don’t You think there Should be separate time Limit and judging criteria for these languages because it makes impossible for java programmers like me to compete in your competitions…

  13. Some Language takes More time of execution then Others for eg compare java and c++ so don’t You think there Should be separate time Limit and judging criteria for these languages because it makes impossible for java programmers like me to compete in your competitions…

  14. Can any one tell me that how to submit the programs procedure … and from where the input file gonna be taken … i dont know which input to use for processing the program and checking out the results
    … plz help

  15. Can any one tell me that how to submit the programs procedure … and from where the input file gonna be taken … i dont know which input to use for processing the program and checking out the results
    … plz help

  16. Can any one tell me that how to submit the programs procedure … and from where the input file gonna be taken … i dont know which input to use for processing the program and checking out the results
    … plz help

  17. Can any one tell me that how to submit the programs procedure … and from where the input file gonna be taken … i dont know which input to use for processing the program and checking out the results
    … plz help

  18. I m keep on trying submitting my code.. but its either showing incorrect or compile error.. its working with no errors in my compiler.. i m using dev-C++ 4.9.9.2… what should i do to successfully submit my code..

  19. I m keep on trying submitting my code.. but its either showing incorrect or compile error.. its working with no errors in my compiler.. i m using dev-C++ 4.9.9.2… what should i do to successfully submit my code..

  20. I venture there are heaps of people like me, who happen across varied strong blogs or web sites by fortune. Your site seems to have got a solid community and a sound blogosphere presence. Its right to have engrossing and different views on issues.

  21. I venture there are heaps of people like me, who happen across varied strong blogs or web sites by fortune. Your site seems to have got a solid community and a sound blogosphere presence. Its right to have engrossing and different views on issues.

    1. Yes. J2SE jdk 6.0 with standard library (excluding some multimedia, network and system interaction classes).

      Starting point for Java programs is public
      static void main (String[] a) method in Main class, which must be defined.

  22. Why is there this one constraint which binds total input over all test cases in shorter range than it could take?
    Example:

    Constraints
    1 ≤ T ≤ 10^5
    1 ≤ N ≤ 10^5
    1 ≤ S_i ≤ 10^9 for each valid i
    sum of N over all test cases won’t exceed 10^6

    What is the use of last constraint?

  23. Why input received is null?

    I have not even submitted my full code… My code is always getting NullPointerException?

    This is frustrating.

    /* package codechef; // don’t place package name! */

    import java.util.*;
    import java.lang.*;
    import java.io.*;

    /* Name of the class has to be “Main” only if the class is public. */
    class Codechef
    {
    public static void main (String[] args) throws java.lang.Exception
    {
    // your code goes here
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    int x = Integer.parseInt(br.readLine().trim());
    }
    }

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