Somehow,Topcoder matches were not getting editorials for a while. SRM 539, SRM 540, TCO Round 2A... I kind of thought that in the case of SRM 539, it got canceled and so did the editorial. One Friday I received the typical email requesting editorial writers for SRM 540. But I did not accept to write it. I think that was the first time that ever happened. I was just too busy that day, and to be honest the work/reward ratio of editorials is looking smaller every new day. It was also quite a random Friday, not really the day after the SRM like it was usual. Then round 2A also did not get any editorial.
The day SRM 541 started, I caught people discussing the previous SRM's div2 1000 in the arena chat. It seemed a interesting problem. I went on to solve it in the practice room, and I liked it. Then I noticed why I haven't heard of that problem before, because of the whole stuff regarding the editorial and me not going for it. I decided to contact rng_58 to ask him if there was nobody assigned to it yet (Since the editorial was not appearing).
Days after SRM 541 finished, I received a reply that yes, I can write the editorial for SRM 540. But seconds later I received a far more interesting email asking for writers for basically all the matches that didn't have an editorial : SRM 539, TCO round 2A and SRM 541 (540 was already assigned to me). That was fortuitous, wasn't it? The email was pretty specific about the possibility of writing many of them. At first I asked to write round 2A's editorial and postpone SRM 540's because I already had written looong explanations for the two first problems, and just a new problem seemed like less work. I was wrong.
TCO round 2A
After being able to get assigned to this round, I made it a priority to finish it because it is a tournament round and SRM 540's was already delayed anyway... Noticed that when I was assigned to write this round I forgot to ask for help with the hard problem. That was a mistake. I ask anyway. Eventually, I receive a quick explanation for it.
And boy did I need it. This hard problem is probably the hardest problem I had to solve this year.
Even after you manage to get close to the solution, (and it requires you to be very creative with meet in the middle) you still need to solve the sub-problem. rng_58 talked about "doing Karatsuba like in SRM 518". Which was a bad sign, because I remember writing the editorial for SRM 518 and I also remember not actually getting anything about the hard problem from SRM 518 and somehow still managing to write an editorial for it.
I hesitated. For a long time I tried to do the subproblem doing anything other than Karatsuba or the transform method. Eventually, I gave up. I then had to somehow think of a way to solve it by Karatsuba or a transform. But again, I remember SRM 518, and I remember how the Karatsuba or transforms came out of nowhere. This time, I was not actually given the actual transformation, so I had to think of it by myself...
I found out that I must be very good at explaining problems o_O. Somehow my explanation of SRM 518 helped me find the way to come up with a transform in round 2A. This was fun.
Anyway, I tried to change my style for this editorial as an experiment. I also added those special tip boxes. I think that in case of 2A, I overused them. But I also think this editorial is the best I wrote in a while. Unfortunately, I took far more time than I planned and was off 24 hours from the deadline, that cannot be good. I just did not expect the hard problem to be so hard.
I figured that I should probably write this editorial. I was already writing more than one editorial. It seemed like no one else wanted to write any editorial. The government imposed a completely irrelevant holiday which gave me lots of free time. And it was my responsibility to write this match's editorial as I wrote 3 problems, specially the one that ruined the whole match.
I did not want anything to do with this match. Hence the reason I did not even make a blog post here. It was such a mess. So I was pretty unmotivated here. Then we have the fact that I always find it difficult to explain my own problems (all of them look pretty obvious to me :). Adding up that I was exhausted after 2A, I am quite sure this editorial is pretty lame and low quality. I tried to exercise the new style as well.
It was actually 5 days after I was assigned this editorial that I ended SRM539's editorial and looked at the div1 hard from SRM 540 for the first time.
I somehow had forgotten that the div1 medium in this problem set was very hard and I left it unsolved. So, when I noticed that such div1 medium had returned to my life I was worried.
Both the div1 medium and the div1 hard gave me quite a lot of trouble this time. I was planning to finish this match before May. But it could not happen. After trying many things on div1 medium, I noticed that, quite disastrously, I was solving a completely different misinterpretation of the problem. But the real version of the problem was still quite difficult. At the end I went desperate and googled for help. But I could not find anything, except some pages in Japanese. Google translator is not awesome and the explanations I found were vague to begin with, but I somehow managed to understand it!
And I felt so stupid afterwards. Because using inclusion-exclusion to calculate sums is so simple even in 3D and it is a typical thing to do to improve dp run time in 2D. The only difference was that this was in 3D, and even so, it is not a big difference.
The hard was more complicated. The first explanation I received was not very clear. I ended up learning way too many things from bmerry's code.
I kept the style. I think this editorial turned out to work quite great. That I spent so much time on those two problems meant that I had a lot of things to say in the explanations.
So, when I finished SRM 540 I was pretty sick of editorials already. Yet I noticed that SRM 541 did not get any editorial yet. Turns out that nobody really wants to write editorials anymore... So I offered myself to do it. I had some time to rest because I was not assigned the editorial immediately after I finished 540.
Unfortunately, when the holiday yesterday I went back to class and someone was preparing a shock surprise to keep me busy doing homework. This screwed all the time I planned to use in writing the editorial. This time the division 1 hard problem was actually easy to understand, but I did not rush to write the editorial because I thought I was going to have time... That was a mistake.
At the end, I had far less time than I thought to finish this editorial. I was also sleep deprived. It seems that the problems were not very explanation-friendly either (or was it just the sleep deprivation's fault). I could not even find a way to use the new style.
I think this editorial is quite lame. There were many times in which I felt like I was just describing the solution instead of how to come up with it. Which is something that I really hate. I might even redo everything using the wiki once I clear up my mind.
Unfortunately, since I could not finish SRM 540 and 541 before May and worse, the SRM 537 prize payments were not approved, I could not accumulate a good amount to cash on May. I think I will starve. :(