SOI Camp 2023 in Sarnen

26 participants from Switzerland met in Sarnen to train together for one week.

Charlotte Knierim

26 participants from Switzerland met in Sarnen to train together for one week (11.02.2023 - 18.02.2023). They were accompanied by a delegation from Ireland and one from Slovakia. In many lectures, contests, and other activities they sharpen their skills in algorithms and practice to apply them in challenging problems.

Each day, some of the participants write about their experience. More photos can be found on flickr.

Sunday, 12th of February (Isaac, Fionn, Ayushi)

After waking up at the unholy time of 7am, we conjured enough strength to make the trek down to breakfast. There, we received the nourishment necessary to tackle the inevitable difficulties that were soon to be laid out Infront of us. After the first few lectures, I felt my brain turn to mush. It’s like my brain cells took an early morning siesta and forgot to come back. A bonus lesson was that reading tasks properly often helps a little bit in solving them. The lectures not only taught us the solutions but the thought process to find them ourselves. In the next few days, I hope to be just as inspired as I was by the lecturers today. No excuse for brain mush now!!

Thanks for having us and good luck in IOI 2023 - but maybe not too much :) !! Signed- Your favourite Irish delegation.

Monday, 13th of February (Elias)

Monday was DP day. Just as every other morning, we got up at about 7:30 (a bit too early in my opinion) and went downstairs to eat breakfast. At 8 o’clock we did warmups. There was a task about bridges and one about two-pointers. Everyone could choose a task to solve on paper in 30 min.

These warmups were a good way to practice for 2T (the theoretical part of the second round) as the leaders were so kind to grade our solutions and give us feedback so we could improve. Afterwards the lectures started. Most of the people in our room were part of the Expert Track. We were really lucky as Petr, a former Russian participant and Codeforces Legendary Grandmaster, who now lives in Switzerland and also helps at SOI was our lecturer for most of the morning. We mostly looked at bitmask DP, a quite slow O(2ⁿ) but very powerful variant of dynamic programming. (It was also required to solve the second hardest problem at the final contest at the end of the week.)

In the afternoon we had another practice contest where we could apply the things that we had learned during the day. Right after the contest we ate dinner and listened to some interesting seminars where leaders talked about some interesting topics that they had experience with (not necessarily competitive programming related). I listed to Misof’s seminar about dijkstra optimizations in real world maps. After the seminars there was a bit of time to play some card games before going to bed.

Tuesday, 14th of February (Dario, Théo, Andrej)

After a nutritious breakfast the solutions of the last day’s dynamic programming contest were presented. They presented the solutions of four tasks, the hardest problem was quite hard to come up with. Then, we got time to upsolve tasks until lunch, which was at 12:15.

Foxtrail am Excursionday

We all travelled to Lucerne afterwards and were split into groups of four participants + two leaders. Each group did a Foxtrail which lasted about three hours. We got to visit different locations spread across Lucerne and solved small riddles at each of them. Unfortunately, we weren’t really able to enjoy our view as the fog limited it to 200 meters. Once we were asked to go into the direction of the famous mountain Pilatus, which we of course were not able to see and then had to google its location. It was really cold outside and we personally were happy to be back in the warm house by dinner time. We played werewolves until late into the night.

Wednesday, 15th of February (Ursus)

This day was again a normal lectures-day, but today, the main subject was “Queries”. We get later to this subject, since every day has to begin with a great breakfast. I ate a very good muesli and after that, we had warmups.

With the warmups done we split up into the three groups and started the lectures. The expert tracks hadn’t have queries as the main topic but probability-theory. In the other tracks the participant learnt very useful queries-structures i.e Segment-Trees and Fenwick-Trees. Binary-search was also a topic.

After lunch we had another lecture. But the big event that day was obviously the contest after that lecture! We had three hours to solve four problems themed around Segment-/Fenwick-Trees and binary-search (queries). It was exhausting, so we quickly had dinner afterwards.

Well, I didn’t like the food, so I and Elias went to the store and bought some sandwiches. We also bought a Kinderegg for Vivienne which was actually very appropriate, because we had a probability-problem with Kindereggs in the lectures. But the toy inside the egg felt more difficult to solve than the contest, so we had a little competition of who can solve it the fastest. As I write this blog, I can’t remember what we were thinking at this moment. It was a funny evening though!

Some people played Tichu, but at some time we went to sleep. Only one day until the I-Cup.

Thursday, 16th of February (Mark)

picture from the picturehunt
Participants in a plane
participant pyramid

Today was a special day, because it was the no-laptop-day (we still used them). In the morning we practiced solving tasks theoretically. We started by solving them in groups and then writing the proof down on paper individually. After the solving, we had solution presentations, with the intended solutions and how the scoring works. Then we had our well earned lunch. After lunch there was the most painful part of the day. We had to correct the solutions of the other participants, which was hard because of ridiculous handwriting and nonsensical omissions. Afterwards we received our own tests and saw how we did and what we needed to improve.

In the afternoon we had the photo hunt event, in which we were randomly put in groups and had to take funny pictures at random locations. It was nice except for the fact that we had to go up a hill that did not have a nice path, so our shoes became very dirty. It was still very fun to come up with a bunch of creative ideas for photos and see other people take them.

After dinner we had some seminars. We could choose between a lecture about the Axiom of Choice, Quantum Physics and Josia’s Matura Presentation. Because the I - Cup was scheduled for Friday morning at 8 am, I decided to go to bed at 11pm instead of playing games until 1am like we usually did, in the hopes of not being sleep deprived during the I-Cup.

Friday, 17th of February (Vivienne, Hannah, Zsófia, Hongjia, Jasmin)

After waking up from a long and relaxing sleep, everybody was excited (and prepared) for one of the most important events of the camp - the I-Cup (or Éire-Cup). Starting from quarter past eight until quarter past one, the 5 hour contest went as fast as a lightening. The 7 problems formed a helpful review of knowledge learnt in this camp and got us better prepared for the second round. These problems were nothing near easy and obvious in the first second, but they became very interesting when one thinks deeper into them. The solution presentation was in the afternoon, where the problems (and their tricky solutions) were explained by leaders. After this we went to take group pictures.

We then played a round of Werewolf (where we totally always accused the right people) and got ready for the announcement of prizes and ranking. We also had the presentation of the pictures of the photo hunt from the previous day and enjoyed looking at cat pictures.

Now the final evening started. Some of us decided to go for a run so that they will get awake again. After those sport enthusiasts returned, we played one final round of Werewolf which lasted very long. To be exact, we finished at about 2 am. Now, some had the great idea to go for a nice night swim in the lake. Because the slovaks left at about that time, we decided to accompany them and then split off to go to the lake. The lake was quite cold but it helped when you were trying to stay awake.

After this successful experience we went back home, played some games, some went to sleep, some didn’t and the final evening turned into the final morning.