Problem link — https://codedrills.io/contests/amrita-icpc-practice-session-7/problems/alibaba-and-thieves There is an editorial, but it just describes the algorithm instead of the idea (or I just don't get it). Can anyone please describe why is this correct? Also, if there are more problems where we need to sort some intervals and do something greedily, please share.

I want to practice some previous year OI or ICPC regional problems, but most of them are obviously quite hard for me,can anyone suggest me some OI's/regional contests which I can start solving to improve at this level,or in other words what are some doable olympiads for a high expert or a low CM?

A weird though came to my mind while writing binary search that why don't we use the geometric mean of start and end instead of arithmetic mean, I mean what would be the time complexity and why don't we use it?

I can generally solve 1800-1900 rated questions on cf contests and 2000-2100 rated questions while practicing, but I can't solve anything higher than that, I need some suggestions on how to get across this plateau, can you guys suggest me a way to practice on cf or some other ojs, I want to get above average and am willing to put enough effort as I love doing CP, I just need a fair strategy.Also it would be of great help if someone has a list of good problems to try of rating (1900-2400) range.

I was solving a question and a thought came to my mind which I think is may be worth sharing,I have a suggestion that there should be a timer associated to every question, so that we can precisely measure how much time it takes us in practice to solve a question, I know we can simply set it up ourselves but still think it would be a great feature, please share your opinions on it too.