Hello Guys ! I want your help regarding specific type of problems that I am unable to solve Below are the three similar problems and when such problems comes during a contest or even when I am practicing I am unable to solve them, can you please guide which topics can I learn to have a good grip on such problems or share similar problems so that I can get used to them and learn the concepts required to solve them. Thank You !

Below are examples of problems in which I face difficulties. After seeing such problems I don't even have a direction to think in

https://codeforces.net/contest/1776/problem/L https://codeforces.net/problemset/problem/1860/B https://codeforces.net/problemset/problem/1836/B

Your Help and Guidance would be highly appreciated