Hi guys.

Today, I looked at my profile and realized I had 61 friends, and for some reason that number encouraged me to make a blog about it. We are going to analyze how I got to being a friend of 61 people and how I personally feel about it.

How I got here

I made this codeforces account in February 2023 and immediately started doing expert level performances in contests. At first, I wasn't fully aware of my potential yet. Having a lack of understanding and a lack of confidence, I named my account Iamdiv5. Initially, my only friend was I myself. I started doing pretty well in the contests, I was getting ranked around 1000-2000 most of the time. Out of the blue, I was blue. But blue wasn't feeling right with me, it made me feel out of place. So for the first time in codeforces, I wrote a blog in codeforces titled "How to escape Blue". There I made some new friends who I never talk with. But again, just because we don't talk doesn't mean we can't be friends. Otherwise, mute people won't have any friends. So anyways, I got some advice on how to get out of blue and suddenly, I was CM. People started confusing me for some random dude in some university, so I set my university name to the university name of that dude. I gained a lot of friends that way, and suddenly I have 61 friends

How I personally feel about having 61 friends

Well, 61 friends is not as good as having 67 friends. But regardless, I don't really have much to say about how I feel because it doesn't really change my life a lot. I think if this number increased tenfold I might start feeling something

Some off-topic things kind of relevant to this blog

You might've read a bit earlier that I am actually a div5 participant. This is definitely my only codeforces account and I definitely don't have any alts. Technically my rating should be in the negatives but you know, some things happen in this world that you can't just explain, supernatural stuff.

And the second thing you could ask is am I still sad because of no girl ever going to love me. Well, after watching some short videos, I agreed that I'm too old for a relationship and I probably should get married at this point. So yeah, that's depressing.

I hope you now understand how to become a friend of 61 users and that you liked this blog.

In the last round (round 1048), I solved the (2138C2) Maple and Tree Beauty (Hard Version) using divide and conquer method and NTT. The problem could be solved by doing binary search on the length of the LCS. For that I can precalculate the number of nodes at every depth, afterwards assign all nodes of a certain depth either white or black color. I can check whether it’s possible by calculating all possible subset sums using NTT and divide and conquer. But every search I would have to calculate NTT using divide and conquer technique which would get me TLE.

To bypass this repeated calculation I tried a modified method of DnC. At first I calculated the NTT for the left subrange for divide and conquer. Afterwards I checked if I only considered the left subrange and could get a common prefix string of that range for the tree. If I could, then I moved to the right subrange, otherwise move to the left subrange. And afterwards repeatedly execute this process by dividing that subrange into left and right. This made sure that I am calculating divide and conquer NTT for the at most twice for each subrange of DnC. However, that also meant that the other half wouldn't be traversed. Making it equivalent to calculating the answer for the whole tree just once.

This was definitely a overkill and not the intended solution, but I knew it could be solved with DnC NTT so I just did. It was fun doing so. Did anyone else try the same idea?

When I created this account, I was beyond division 4. I was division 5. Today I have reached division 1, but still, deep down in my heart, I still belong in division 5. So you can be division 5 too! Don't lose hope. Life is not a race, life is a marathon.