Links..

Online judges

ACM Live Archive, has many problems from past ACM/ICPC regional contests and world finals.
Arbiter, online judge at Sharif University in Iran.
FZU Online Judge, about 500 problems.
Harbin Online Judge
HDU Online Judge, has virtual contest features and quite a lot of problems.
Hunan University ACM/ICPC Online Judge, seems to have a lot of problems from regional contests. Unfortunately a lot of the material is in Chinese.
Google Code Jam, here you can practise on problems from previous competitions. They allow you to code in whichever language you want, which is really nice. The interface is excellent compared to most similar sites.
Jilin Online Judge
Lviv Online Judge, over 100 problems and expanding. Unfortunately it is only in Ukrainian.
Moscow Online Judge, few problems, but all of are of a high quality.
Peking University Online Judge, more than 2220 problems.
Programming Challenges, a judge that contains all the problems in the book of the same title (by Steven Skiena). The problems are a selected subset of the problems from the UVA judge.
Saratov Online Judge, over 200 problems, most problems are also rather challenging.
Sphere Online Judge, over 500 problems, this judge supports over 25 different programming languages. It excels in this area. This is a widely used online judge.
TJU Online Judge, over 3000 problems. Most are from old regionals or similar. A cool feature on their judge is the ability to have virtual contests, and since they have a lot of old regionals, this is a very useful feature for team practice for upcoming ACM/ICPC contests.
TopCoder, TopCoder is not actually an online judge. TopCoder is an organization that arranges programming contests. They have their own arena with practice rooms and a lot of problems from previous SRM’s (single round matches). Moreover TopCoder arranges matches almost weekly, often with prizes to the best scoring contestants. Many people practice at TopCoder, and it is also highly encouraged.
Ural Online Judge, over 500 problems, in general most problems are quite difficult.
USACO Training Program Gateway, this site is intended for high school students, but is in fact used by many others. They have a nice training program with tutorials, and reference solutions that you can see once you have solved a problem. Their training program is highly recommended.
UVA Online Judge, more than 2000 problems available. All problems on this site are from this judge.
ZJU Online Judge, over 1800 problems. Note that this judge supports only C and C++.

Useful sites

Algorithmist, here you can find explanations of many problems and also classifications. There are also nice tutorials about different subjects. Also they have a calendar of different programming contests. You should really check this page out!
Felix Halim – Hunting UVA problems, Felix Halim has a great site where you can Hunt UVA problems. One great feature is that you can view “the next 20 easiest problems for you”. This is of an immense aid in helping you find problems that you are able to solve. You can also find a graph that shows your problem solving progress. He also keeps ranklists for all countries in the world. All in all his site is greatly recommended.
GMU ACM ICPC Code Repository, solutions for different problems on the UVa online judge, ACM/ICPC regionals, and also explanations of various techniques such as dynamic programming.
Steven Halim – World of Seven, at this site you can find hints for many of the problems. There are also some nice tutorials that will help you learn new algorithms and problem solving skills. It is also a good site to visit if you are stuck on a problem and need a hint. He has hints for around 530 problems from the UVA judge.
Igor Naverniouk’s site, Igor has a lot of experience in solving problems at the UVA judge. At his site you can see how he has has classified his solved problems, and in some cases you can also get hints. His problem classification list is often very useful. His library of algorithms (in C++) is very useful, and is definitely worth a look.
Waterloo Programming Contests, this is the local page for contests held at the University of Waterloo in Canada. Here you will find a lot of great problems (most of them are also on the UVA judge), including solutions, input and output. Most solutions are of a very high quality. If you are stuck on one of their problems, it may be a good idea to take a look here.
Mesmay’s ACM-ICPC Resources page, here you can find hints for many of the problems of Volume I at the UVA judge. You can also find extra input and output for these problems. Furthermore there is a section concerning many of the standard algorithms. This site is mainly useful if you are stuck on one of the problems of Volume I at UVA

TopCoder tools

otinn.com, has myriads of different statistics from TopCoder competitions such as “country statistics”, and various interesting features such as “TopCoder duel”. If you are bored, there is always something to look at there.
Micromatch scores, compares the performance of two competitors using the problems that both have faced.
Division summary, Felix Halim has made a very nice overview of division summaries from TopCoder algorithm competitions.
Division summary, same as above but with a different interface.
Algorithm rating graph comparison, can be used to compare algorithm rating graphs of any number of competitors.
Random Coder Stats, shows random but still very interesting statistics about a coder
TC Utilities, here you can calculate predicted ratings, expected value of prizes and various other things.
Country Statistics, has ratings of countries in terms of their performance in TopCoder algorithm competitions.

Google Code Jam statistics

GCJ 2008 Statistics, a lot of different useful statistics over GCJ 2008.
GCJ Round 2 scoreboard, an unofficial scoreboard relating contestants to their TC handles (by the topcoder zibada).
GCJ Round 3 scoreboard, as above but for round 3.