For those who strugled to solve div2 A problem this video may help you to understand it
https://www.youtube.com/watch?v=8rhnRzicPlc
You can write your thoughts on other problems in the comments
UPD: For those who strugled to solve div2 B problem this video can be useful:
thank you so much. much needed
Auto comment: topic has been updated by ismoilmirzouz (previous revision, new revision, compare).