# Internet Problem Solving Contest

## Welcome to IPSC

Internet Problem Solving Contest pushes the boundary of what is possible in programming competitions. The problem set has a wide mix of problems that includes both challenging algorithmic problems and various unusual kinds of problems which will test your outside the box thinking. Every year, thousands of contestants gather to compare their skills, learn something new, and have fun. Will you join us too?

### IPSC 2018 is over

IPSC 2018 took place from 6 October 2018, 15:00 UTC to 6 October 2018, 20:00 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 ♪ ♪ ♪
shik, step5, peter50216 from Taiwan, representing Google / UT Austin / 🐰🏠
Team FAILED TSTST Day 3
Benjamin Qi, David Hu, Walden Yan from United States, representing Princeton HS, Lynbrook HS, Avon HS
Open Division (individuals)Secondary School Division (individuals)
Team usagi
Yui Hosaka from Japan, representing The University of Tokyo
Team saba2000

If you missed the contest, or if you already want to prepare for the next one, don't worry! IPSC 2018 is available as a virtual contest in the Training Area, together with all past IPSC contests since it began in 1999.

### What makes IPSC different?

The IPSC rules might not be what you're used to:

• You can download all input files immediately and you only need the correct output, so you can use any programming language or even solve problems by hand.
• You can participate as a team of up to 3 people, or as an individual. Individuals have a separate ranklist.
• Secondary school students are also welcome, and have their own ranklist.

But the secret sauce is in the problem set. 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 these problems sound interesting, try solving them in the Training Area, browse through the Archive for other problems like them, and join us for the next IPSC!

### 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 2018 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.