It's a cool idea, but I don't completely agree with your problem choice. I think that problems in the range div1 B-C will have a much larger audience. Maybe you should setup a polling system or something?

I really like where you are going with this. It would be nice if we could see some DIV2 problems aswell.(B-D) Cheers

Oh I'm glad I'm getting feedback. I certainly plan to do a wider variety of problems in the future. I just wanted to start with this one for the reasons I explained in the video :D

Learning from a video is a very nice way to learn. You show us how you reach the solution and that is something you don't find too often, even when you read the editorials of the problems. So congratulations and thank you very much!.

rad channel man

you got yourself a subscriber

Dope channel, I love how you explain your thought process instead of just going over the solution so it will be more helpful for solving different problems in the future. Thanks a lot Alex.

you should record the thought process of all the problems of a particular contest after the contest is over and release it just like editorials, especially div2 C, D, E.

I'm also open to requests, if you have a some particular problem you'd like me to do. I already got a few so it's only fair I tell you guys that I'm open to that.

The reason for the WA is that is possible that the root node and its children are deleted and that the second dfs then never visits the part of the tree that isn't deleted. Small challenge case: '7 5 2 2 2 2 2 1 1 1 2 2 3 3 4 4 5 4 6 5 7' (answer is 2, but first attempt returns 1).

Btw I liked the idea and the video. You solved the problem in a somewhat different manner than I did. For me personally the explanation+coding could have been a lot shorter, but then again, I realize that this may not be true for the target audience.