1.Q: Where does my program input from and output to?

A: Your program should always input from stdin (standard input) and output to stdout (standard output). For example, you can use scanf in C or cin in C++ to read, and printf in C or cout in C++ to write. User programs are NOT allowed to open and read from/write to any file.

More should be noted about I/O operations in C++. Due to their complex underlying implementation models, cin and cout are comparatively slower than scanf and printf. If a problem has huge input, using cin and cout will possibly lead to Time Limit Exceed.

2.Q: What are the compilers used by the judge? What should I notice when using these compliers?

A: GCC 4.3.3(Debian 4.3.3-5) are provided for G++/GCC.The compilation options are

gcc runid.c -o runid -O -fno-asm -Wall

g++ runid.cpp -o runid -O -fno-asm -Wall

Notice the difference between GCC 4.3.3 and other compilers to avoid Compile Error when using G++/GCC.

• The return type of the main function must be int, otherwise it will cause Compile Error.
• Remember to include <cstdlib> and <cstring> when using some functions in these library,GCC 4.3.3 won’t include them automatically when only <iostream> is included.
• For 64-bit integers,only long long is supported.You should use “%lld” as the format string when using scanf or printf.

JDK 1.6 are provided for JAVA.The compilation option are

javac -g:none -Xlint Main.java

java -client Main

A Java program must be submitted as a single source file. Apart from complying with restrictions imposed on all submitted programs, it must start execution in a static method named main in a class named Main, otherwise Compile Error will be caused.

Java programs are allowed to run for THREE TIMES the time limit of GCC/G++, ans to use TWICE the memory limit of GCC/G++.

3.Q: What are the meanings of the judge's replies?

A: Here is a list of the judge's replies with their common abbreviations and exact meanings:

Judging/Waiting: Your program is being judged or waiting to be judged.

Rejudging: Your program is waiting to be rejudged.

Accepted (AC): Congratulations! Your program has produced the correct output!

Presentation Error (PE) : Output Format Error.Your output is the same as the standard output when all blank characters are ignored. Check your output for spaces, blank lines, etc. against the problem output specification.

Wrong Answer (WA) : Correct solution not reached for the inputs. The inputs and outputs that we use to test the programs are not public. Some problems with special judge may not reply "Presentation Error", replaced by "Wrong Answer".

Runtime Error (RE) : Your program failed during the execution (segmentation fault, floating point exception...). The exact cause is reported except Java.

Time Limit Exceeded (TLE) : Your program tried to run with too much CPU time. Java programs are allowed to run for THREE TIMES the time limit of GCC/G++.

Memory Limit Exceeded (MLE) : Your program tried to use more memory than the judge default settings. Java programs are allowed to use TWICE the memory limit of GCC/G++.

Output Limit Exceeded (OLE): Your program tried to write too much. This usually occurs if it goes into an infinite loop. The output limit is 32MB.

Compile Error (CE) : The compiler could not compile your program. Of course, warning messages are not error messages. Click the link at the judge reply to see the actual error message.

Restricted Function (RF): Your program tried to call restricted functions. For example, maybe you have tried to open a file which is forbidden on OJ. It may also caused by Runtime Error (e.g. maybe a pointer point to wrong funtion), just consider it as Runtime Error in this situation.

4.Q: What does the phrase "Special Judge" under the problem title means?

A: When a problem has multiple acceptable answers, a special judge program is needed. The special judge program uses the input data and some other information to check your program's output and returns the result to the judge.Be carefull that Format error may cause WA not PE for such problems.

5.Q:My program can get right answer for all data in the problem with my computer,but when I submit it,it get WA.Why?

A:After your source code has been submitted,judgers will use data which is not public to test your program.If you get wrong output for these data,Judgers will reply Wrong Answer.So your program must have some bugs,please check your program.

6.Q:Some problems which was Accepted when I submit it turn to be Wrong Answer,Why?

A:When judgers find some bugs in test data,they may rejudge all submits.But in a contest,problems never be rejudged from AC to WA.