# Internet Problem Solving Contest

## Welcome to IPSC

The Internet Problem Solving Contest is an online programming competition for teams of up to three people. Each year, hundreds of teams gather to solve challenging problems and test their skills against some of the best programmers in the world.

The problems range from easy to very hard, so everyone is welcome to compete. We also have separate ranklists for individuals and secondary school students. You can use any programming language, or even solve problems by hand. Most of the problems are algorithmic in nature, but IPSC is particularly known for its unusual and fun problems. Here are some of our favorites:

• In one task, your goal is not to sort the input sequence. (2010/A)
• Find three numbers such that x=y and y=z, but x≠z. Impossible, right? (2008/C)
• Sometimes, you don't have to program, you can just play a game. Though that might be harder than it looks... (2013/L, 2009/F)
• The input files don't have to be lists of numbers. How about images or even music? (2013/I, 2012/J, 2009/C, 2008/H, 2007/E)
• Some problems require multiple attempts, because each one gives you new information. (2013/F, 2012/K, 2010/E, 2004/D)
• No one likes ambiguous problem statements, but what about a problem that doesn't have any problem statement? (2012/B, 2011/Q)
• Some tasks are about analyzing obfuscated pieces of code or oddly encoded data. (2013/C, 2006/M, 2003/B)
• Don't be surprised if a task has its own scoring rules. In 2009/D, every wrong answer counts as a bonus instead of a penalty. In 2010/M, your score depends on how well you predict the actions of other teams. And in 2011/M, you just have to take care of a little puppy.
• Multiple problems involve using various esoteric programming languages. (2011/H, 2011/I, 2009/I, 2007/Q, 2005/Q, 2004/G)

If that sounds interesting, you should compete in the next IPSC! Until then, you can also try solving the above problems in the Training Area. Or browse through our Archive and see if anything else catches your eye.

### How to compete

1. Find a team of up to 3 people, or compete as an individual.
2. Read the contest rules and register for the contest.
3. Optionally, take part in the practice session to see how the contest works – especially if you're competing for the first time.
4. When the contest starts, read the problem statements and begin solving.
5. Choose a problem, download its input files, and try to write a program that produces the correct output file.
6. Submit the output file and wait until it's judged "OK" or "Wrong answer".
7. Repeat that until you have solved everything.

### IPSC 2015 is over

IPSC 2015 took place from 20 June 2015, 11:00 UTC to 20 June 2015, 16:00 UTC.

Congratulations to the winners, and thanks to everyone who participated! We hope you had fun, and we're looking forward to seeing you again next year.

Open DivisionSecondary School Division
Team R+T+J
Reid Barton, Tomek Czajka, John Dethridge from (no specific country)
Team ✓ (2+2*2)*(2+2+2+(2/2+(2*2)!)^2) people clicked this link! Why don't you try?
Sunghyeon Jo (17), Jeehak Yoon (17), Suchan Park (16) from Korea
Open Division (individuals)Secondary School Division (individuals)
Team W4yneb0t
Nikola Djokic (22) from Switzerland, representing ETH Zurich
Team
Brian Chen (18) from Taiwan Region, representing IBSH

### Postcard Quest

We still don't have enough postcards from all over the world. Therefore the annual special task remains: You are encouraged to send us a nice postcard. If the postcard arrives before IPSC 2015 begins, your team will be awarded -60 penalty minutes. (Don't forget to write the name of your team on the back of the postcard.)

Our address: KSP, KZVI FMFI UK, Mlynska dolina, 842 48 Bratislava, Slovakia.