SOI Camp 2026 in Sarnen

Saturday, 7th of February

Written by: Aliaksei

On the wonderful first day of the camp, all of us finally had a chance to meet our Olympiad friends, get to know some new participants, as well as cringe about those who procrastinated the second round and didn’t qualify (yes i’m talking to you Austin).

The camp activities started with icebreakers, where we had to answer some questions about ourselves, and try to find who gave a given answer to a question. However, as the array of answers is unsorted, you can’t binary search the answer. Moreover, as everyone is moving around, keeping track on who you’ve already asked might exceed the memory limit. Nevertheless, the best score achieved was 26 correctly identified people which I think is quite impressive.

The next icebreaker was quite a standard one at the camp: teamwork and structural engineering. This year, the had to build a tower out of paper and duck duct tape to balance a very fragile object [1] on. Additionally, every tower will be attacked by an opposing team with a very aerodynamic object [2]. If the object enjoying the view [3] withstands the artillery [4], the builders get more points! So after a lot of folding, balancing, taping, spying on the designs of others, disputing on what qualifies as a tower [5], it was on to the judging. Surprisingly, most towers turned out to be more stable than the whiteboard stands used throughout the week [6]. There were many interesting designs, but the Quack Tower(c) by Alan, Levin, Myriam, Pranav and me turned out to have the best combination of height, style, and the opponent’s bad aim stability.

After that was the food. Last year’s first day dinner was definitely memorable, though not exactly in a good sense. This year, the stakes were truly high, considering the dish was the same as last time, but the cooking team really did succeed. I guess the orgas also did some upsolving in their free time.

The first night went just as expected at SOI - no sleep, just Tichu and other games. For a lot of participants that was their first SOI camp night, but nobody seemed to dislike it as the pattern continued for the whole week.

Sunday, 8th of February

Written by: Alan, Albert

This day was the first normal day, except for the fact that basically none of the participants where late for breakfast. After that, we were able to begin with our first contest on time. We were not used to contests not being delayed like last year. We had six different tasks, not following any particular topic, because we didn’t really have any lectures the previous day.

After this contest, we had another big surprise. The food wasn’t just barely edible, it was actually kind of good, which once again, we were not used to. Before the lectures started, we had some free time. There was a group, that went for a walk to the lake, which some of us joined. Levin, Till and Albert asked some leaders before going, if we could take a cold bath in the lake, but since there wasn’t enough time for that, the idea was not approved. Instead, one leader gave us a ball just before leaving, which Hannah, the leader leading the group, carried for us. I just wanted to add, that the pressure inside and outside the ball, were exactly the same. When we reached the lake, we realized, that we had no time left, so we started walking back home, still not having done anything with the ball, except carrying it. I guess, it was there for emotional support.

After exploring Sarnen, we had our first lectures. We were split into 3 groups based on the ranking from the intro contest. These lectures where held about graphs, meaning, it was interesting, but it’s also really really boring to write a blogpost about it, so I will continue with the more interesting stuff.

At dinner we started realizing, that edible food may be a reoccuring trend during this camp. (Also, edible is an understatement once again, but for last year, it really wasn’t). The evening was kind of special* in the sence, that we did not play blood on the clocktower. Instead we played many different games, for example Crazy Time* , which many people really dislike, for good reasons, so it’s hard to get a group to play it. Luckily, new participants didn’t know it yet. There was also a different, way more important game for some of us, Hanabi, which was one of the reasons why we often didn’t sleep enough, like on the last day, when our sleep was replaced by Hanabi. Also, our plan to go in the lake was accepted a few days later, but not this evening. And on the 3. day, there was a reference in a task to us asking to go to the lake. And after playing many games, most of the people went to sleep early compared to the other days (still, we were tired the next day).

Monday, 9th of February

Written by: Arsenii, Caius

On Monday, we were excited after Graphs Day and had the graph contest in the morning, which went well. We were able to practice implementing different graph algorithms. Afterwards, we had lunch, and our group had to do the dishes that day. After that, we had a short break followed by a solution presentation, which was very interesting.

Until the evening, we had lectures about different DP problems, which I found interesting, even though some concepts were hard to grasp. We learned about DP patterns such as LCS, LIS, DP on trees, and knapsack. We also had some snacks in between. After dinner, we had some free time to play Tichu and prepare for the DP contest the next day, and then we went to sleep.

It was an exciting day during which I learned many new algorithms that I still need to practice implementing. However, this day and the whole camp overall—gave me direction and helped me set the goal I am working toward now.

On Monday, the camp had only just started out, so we were still getting used to the schedule. In the morning, after breakfast, we had our first topic-oriented contest, where we could practice the skills we had learned on the previous day. After the contest, we had lunch and got to know the other participants a bit better. Fortunately, none of us had to do the dishes, so we could actually enjoy our free time. In the afternoon, we had some lectures about dynamic programming, which were very educational, as well as some time for solving tasks on our own, only interrupted by a short snack break with some delicious chocolate cake. After dinner, we were again spared from kitchen duty, so we spent a lot of time playing games with other participants, which was tons of fun. That evening, all of us went to bed relatively early (at least compared to the days to come), because we wanted to be ready for tomorrow’s contest.

Tuesday, 10th of February

Written by: Myriam

After a good night sleep (although quite short for some of us), we went to breakfast, some of us had to clean the dishes, and then the DP contest started. For the expert track, the contest went quite well (as the opposite of the previous day, most of us got non-zero points and solved a task, and some even full scored the contest!) But to be fair, the first task was a direct application of heavy light decomposition, that we saw on Monday, and was even a special case with a nice implementation, and the third task was an application of lca. (I don’t remember the second one that much since I struggled with debugging my lca.) In the afternoon, we had a scavenger hunt. How did it go? Well, I guess that depends on the group. We got the first clue at the camp house, it was a message in morse, and it happened that Tamara has a great app on her phone that helps with decoding a bunch of different types of code, like morse or Braille. So, we went to the place we were supposed to go, that is some house on a small hill beyond the camp house, where we took the group pictures on Friday. There, we got some hints from Bibin (he had two sheets of paper taped on him, that said “I ♥ numbers” and “I ♥ lv03”, with lv03 being a Swiss coordinate system (not to be confused with lv95)). He also gave us a set of coins with numbers on one side and Braille (numbers?) on the other. Mostly every team struggled with this clue, and we were the last group. After calling Benjamin to get a hint, we figured out something (don’t ask me how), and we got coordinates that pointed to the top of a hill at the other side of Sarnen, so we went there (great idea, right?). On the way there, we met Benjamin on a bike, and he seemed a bit confused when we told him we were going on a hill. But can you take human reactions as actual hints? I don’t think so. So we went to the hill, and once we were on the top, we realized it couldn’t be the right place, because there wasn’t anyone. So, we called Benjamin (recursive pattern?), who told us that we probably used lv95! He then gave us the real coordinates, which were actually in the village of Sarnen. The time we were there, more than an hour had passed since we left for the hill. Then, Benjamin told us to skip a few hints so we could catch up. That actually made us miss the piece of cake! The next hint was “Ask the lion for a riddle”, which obviously meant we had to go to the pharmacy, because it was called “TopPharm Löwen Apotheke” (for those who don’t speak German, like me, Löwen means lion) (and we didn’t even have to ask Benjamin for more hints, only another team!). There, we got a children puzzle (estimated age: 4), with a graph drawn at the back, and a red cross to reach.

Once there, we found a paper with a link: https://ben.soi.ch/remix.mp3. This remix actually became a hit during the week! After being slightly confused by the music, and the possibility to directly go to the fire station (next to the camp house), we met Ursus’ group, and just followed them until a place, were we didn’t find any clue, and we were about to do Nandor’s motivational speech about the scavenger hunt, when someone found a sheet of paper with six images (clearly AI generated, the code is not actually on the screen):

Somehow Ursus’ team figured out where to go, and we started following them until they started running, and I think it was Arsenii who decided to run. At some point, we thought we just had lost him, but he found us and told us we had to get to the camp house. Once there, someone asked us if we found the monster (which monster?) and told us it was the egg, because of “Mehrzweckanlage Ei” (the name of the camp house, which means multi-purpose facility egg). So, we told Benjamin that and he let us in. We weren’t even the last group! In the evening, we played games and probably went to bed a bit earlier than the other days (probably because of the exhaustion due to the scavenger hunt and the nice hike on the hill), but we still played a bit of blood on the clock tower.

Wednesday, 11th of February

Written by: Seraina

It has become a trend that fewer and fewer people manage to get up and eat breakfast in time (this might or might not have something to do with the really looong Blood on the Clocktower game the night before). As a result, the team contest actually started ten minutes late. However, it was still a really fun experience to solve problems as a team using only one computer. For one particular team, it was quite a challenge as they had to debug four problems simultaneously in the last hour (they managed to do it, yayy!). For each problem we successfully solved, we got a balloon of the corresponding colour. So, in the end, not the team with the most points won the contest, but the team with the most balloons blown up. After a tasty lunch (Riz Casimir), we enjoyed some lectures on data structures as preparation for tomorrow’s contest, while the leaders tied up all the balloons and hung them up. The advanced track was getting really tired, which is why some of us played a few rounds of Tichu instead of actually implementing a lazy segtree (they were just saving the fun implementation for tomorrow’s contest, obviously). After dinner, we started playing some games again. The first round of Blood on the Clocktower was unusually short, as we got tricked by the minions, but the second round was interesting and confusing until the very end, when the townsfolks managed to win. As a result, we all went to bed a little too late. Honourable mention: the chocolate mousse we got as a snack was very tasty!

Thursday, 12th of February

Written by: Arsenii

On Thursday, we finished all the lectures for the camp, and it was time to practice our skills. After breakfast, our group had to do the dishes, but it didn’t take long. Afterwards, we had a Data Structures contest where we practiced implementing binary search and segment trees. When the contest ended, we had lunch, followed by a solution presentation. I was surprised that I understood almost all the tasks and was able to upsolve them in the evening.

We had a lot of free time that day, so we played many board games like Tichu. We also had time to upsolve the tasks and prepare for the iCup Pro Max. After dinner, we went to sleep. I was really happy at the end of the day because I was able to implement a segment tree during the contest, even though I didn’t score many points overall.

Friday, 13th of February

Written by: Andrej, Gilles

The long-awaited iCup Pro Max took place on Friday. Participants had five hours to solve eight tasks simulating the conditions of the final round exam at least in length. The tasks ranged from determining the sweetness of molecules to flooding the Alps of Cheeseland. However, not everything went as planned. The task Art College could be brute-forced in O(n³), relying heavily on the CPU cache. Conversely, some people struggled to get their O(n² log(n)) solution to pass within the time limit. The grader was also feeling very generous today, as it decided to give 400 points to Andrej’s Reversals solution; but unfortunately this was a bug, since his solution was so bad that the checker was printing the result in scientific notation, which got misparsed by the grader as a much bigger number than it actually was [7].

After lunch — if we can still call it lunch when it’s served after two o’clock — the participants gathered next to Burg Landenberg for a photoshoot. As well as taking group photos, a portrait of each participant was taken. These would end up serving a very crucial purpose a little bit later.

Finally, it was time for dinner, and the kitchen team seized the opportunity to try to get rid of all the leftovers from the previous days. After dinner, everyone gathered for the announcement of the iCup Pro Max results. But unfortunately, we first had to enjoy an absolutely epic live performance of How do I get to the fire station? by our amazing leaders. After witnessing this once-in-a-lifetime performance, it was time for the traditional grader visualisation, showing the evolution of the scoreboard over the duration of the contest, where the aforementioned portraits were shown [8] each time someone got a full score. The winners and those who had performed exceptionally well during the previous day’s contests could then choose a prize among an amazing [9] selection of books.

How do I get to the fire station???

Even though it was getting late, the grader was put up again with a single task called Ranking Reveal. As input, a list containing the rankings of a contest plus some garbage data was provided. The task was to order and clean up this list. Little did the participants know that their code would be tested against the actual rankings of the second round, which had not yet been released, so a small group of participants had a lot of fun manipulating the grader’s feedback to try to extract information about the long awaited leaderboard.

Saturday, 14th of February

Written by: Fabian, Kailash

After a few days, which felt like seconds, it was Saturday already, the last Day of the Camp, so some decided to make the best out of the remaining time and stay up the entire night playing games (or at least most of the night), some chose Card games, some chose videogames (Hollow Knight: Silksong and Celeste especially). And others did actually want to get some sleep (like us) so they went to bed at like 5 am, as to not be completely sleep deprived.

The following Morning didn’t go as planned for us (we overslept breakfast), but that’s not that important.

After breakfast everybody could make a sandwich, and after that had to help clean (although we weren’t that enticed about it), us two (the ones writing this) first helped vacuum and mop the highest floor(except the bathroom) and after that helped clean out the kitchen, which also meant being able to snack on the leftovers from making sandwiches (I ate so much I didn’t even use my sandwiches that day).

When you were finished with your task you went into the big lecture room, where you wrote your name on whiteboard and if a leader needed somebody, they took the one highest up on the list (kind of like a queue). While waiting I noticed somebody really sus having lost their fight with sleep, and now having switched to fighting the Radiance instead (Looking at you Ursus).

Eventually The Slovak delegation left (I have no idea when exactly). We said our goodbyes and wished them all the best (cause like did I mention already that they had like an 10 hour train ride?).

But then when eventually most was cleaned, we gathered outside so the remaining floors could be cleaned and when that was done, we said our goodbyes and took whatever way we had to get home, and obviously went home, with lots of new friends and a lot of good and memorable experiences, some of which sus or annoyingly catchy.