TO START SOLVING PROBLEMS IN
24 HOURS OJ
Department Of Computer Science & Engineering
of Engineering and Technology.
This article is
especially for the participants in 24 hours online judges
Learn a programming language
want to start programming in 24 hours online judge, the very first step is to
learn a programming language. The most common languages used in the contests and
24 hours online judges are C, C++ (C plus plus), Java (Recently), Pascal. To
start solving problems, you need not to learn all the languages (Although many
programmers learnt more than one programming languages), but you have to learn
at least any one of the four languages very deeply. This is because; when you
will start solving problems you will have to concentrate only on the particular
problem and you will have no time to think about the grammar of the programming
languages. You should have a very well concept of the special features of the
language you have learnt (for example, STL in C++) and you should practice these
features to remove ambiguity while programming. After learning a language, check
the other languages for any special feature that is much hard in the language
you have learnt but very easy to code in that language (for example, in Java it
is easy to use linked list as it was previously programmed (Built-in function)
but in C it is harder as you have to write it manually.). You have to learn the
standard form of the languages.
Choose any of the famous OJs
There are many famous online
judges that can judge your solve 24 hours. Some of them are
You may try to solve any of them.
All of them have there own problem sets. Choose any one of them.
Forget Efficiency and start
solving easier problems
Sometimes, you may notice that
many programmers solved many problems but they made very few submissions (Of
course, they are geniuses). At first, you may think that I should try to solve
the problems as less try as possible. So, after solving a problem, you will not
want to try it again with other algorithm (may be far far better than the
previous algorithm you used to solve that problem) to update your rank in the
rank lists. But my opinion is that if you think so you are in a wrong track. You
should try other ways as in that and only that way you can know that which of
the algorithms is better. Again in that way you will be able to know about
various errors than can occur. If you donít submit, you canít know it.
Perhaps a problem that you solved may be solved with less time in other way. So,
my opinion is to try all the ways you know. In a word, if you are a beginner
forget about efficiency.
Find the easier problems. Easier
problems mean those problems that donít need a particular algorithm as I
assumed you as a programmer who donít know many algorithms. Those problems are
called ADHOC problems. You can find the list of those problems available in 24
OJ in S. Halimís, acmbeginnerís, acmsolverís websites. Try to solve these
problems and in that way you can increase your programming capability. As far as
I found, volume-4 of Valladolid OJ has many easy ADHOC problems.
Facing Compilation Errors?
The first source of compilation
error is the submit process. Earlier, most of the OJ has no special submitting
system. They used mail programs (Yahoo mails, Hotmail systems etc) to get
sources from the authors. These mail systems have many disadvantages. They
append some extra lines at the end of the programs and as the compiler canít
recognize them, they give CE (Compilation Errors). These systems also break a
long line of your program to several lines which may cause CE and wrong answers.
So, if any special submitting system is available for the OJ, use them (For
example, the submitting page of Valladolid OJ).
To know more about compilation errors, check my article at acmsolverís website).
Most of the problems of 24 online
judges are dependent on various algorithms. An algorithm is a definite way to
solve a particular problem. If you are now skilled in coding and solving easier
problems, read the books of algorithms next. Of course, you should have a very
good mathematical skill to understand various algorithms. Otherwise, there is
no other way but just to skip the topics of the books. If you have skill in
math, read the algorithms one by one, try to understand. After understanding
the algorithm, try to write it in the programming language you have learnt
(This is because, most of the algorithms are described in Pseudo code). If you
can write it without any errors, try to find the problems related to the algorithm,
try to solve them. There are many famous books of algorithms. Some of them are
- Introduction to ALGORITHMS Ė Cormen, Leiserson,
- Fundamentals of COMPUTER ALGORITHM Ė Sahni,
Try to make modified algorithm
from the given algorithms in the book to solve the problems.
Donít be pessimistic. Practice makes a man perfect. So,
try to solve more and more problems. A genius canít be built in a day. It is
you who may be one of the first ten of the rank lists after someday. So, get a
pc, install a programming language and start solving problem at once. My only
ďTake programming as a fun.Ē
O., V. Khera, and D. Kotz. The Internet Programming Contest: A Report and Philosophy
R. A., and S. Manzoor. Orientation: National Computer Programming Contest 2000, Bangladesh National Programming
- Ernst, F.,
J. Moelands, and S. Pieterse. Teamwork in Programming Contests: 3 * 1 = 4, Crossroads, 3.2.
M. Bangladeshi Students in the ACM ICPC and World Championships.
T. Guidelines for Producing a Programming-Contest Problem Set: http://wwwpa.win.tue.nl/wstomv/publications/guidelines.html
Mistakes in Online and Real-time Contests by Shahriar Manzoor
Anupam Bhattacharjee is grateful to
Dr. M. Kaykobad, Dr. A. Kashem, Rezaul Alam Chowdhury, Munirul Abedin, Shariar
Monzoor, Rujia Liu, Adrian Kuegel, and Jimmy Mardal, Hasan Shihab Uddin, A. K.
M. Saifun Nabi, Sujoy Kumar Chowdhury above all his family for their helps and
for inspiring him. He is also helpful to all his friends for helping him to
prosper and inspiring him for contests in 24 hours online judge
Anupam Bhattacharjee is a BSc student of
Bangladesh University of Engineering & Technology (BUET). He has
been participating in 24 online judges for long days at Valladolid site
and has made a room in the first quarter of the rank list. His interests
are contests, algorithms, music, and after all computer programming.
Visit him on