Common Problems
C++
The compiler that is used is different than the one used in Dev-C++ or Codeblocks in Windows environment. If you are able, use a GNU Linux environment.
Do not use a main function or do any output. This will mess with the testing system, generating an immediate compile or runtime error. Stick to the class signature that is provided.
If you use global variables or constants, define them in the class body. Leaving them outside the class may result in a compile error.
Be careful with the #define statements, sometimes they can mess things up in a very weird way.
Watch out for implicit casts! Double to int setting will result in a compile error. This is a very common issue.
C#
Do not use a program class or a main function or do any output. This will mess with the testing system, genarating an immediate compile or run-time error. Stick to the class signature that is provided.
The compiler is not Microsoft C#.NET, but Mono. Make sure you read the documentation about some parts in the compiler or the framework missing. Dynamic structures, lambda expressions and other C# modern functionalities are generally supported, but try to avoid them and be careful while using them. Make sure you always preemptively compile your solution in order to avoid any further problems.
Java
Usage of System.out.println or any other I/O in your code may slowdown the execution to that point that some test cases get a time out. Before testing or submitting, double check your code for any I/O operations.
Usage of private classes is not supported. Please stick to the class template provided by the system.
A lot of solutions may fail because of improper usage of a String object. Beware of wrong comparison (== instead of .equals), immutability (s.concat(p) instead of s = s.concat(p)) or some escapings.
