197B — Limit https://codeforces.me/problemset/problem/197/B

It is also an interesting problem for examining your calculus skills without using coding, make sure to check it out.

1714F - Build a Tree and That Is It

its interesting

4A - Watermelon

Dima and Lisa

it was about counting the numbers of string pairs that if they are merged we can make a palindrome from the merged string , we can rearrange the alphabet in the merged string in any arbitrary order I think it's a very well known problem I was fascinated by this problem I don't remember it's name

Kyoya and Permutation

Is one of my favorites, it seems weird at first but after giving it some time and think, it turns into a beautiful adhoc problem. I just love it when seemingly complex problems dissolve into familiar patterns.

1879D - Сумма функций XOR, also the same idea: 1957D - Битовое неравенство

Others: 1945G - Повар и каша, 888G - Xor-MST

Also the Name of this problem: 1983E - Я люблю шары

https://codeforces.me/contest/4/problem/A

Final Countdown

Problem C from https://codeforces.me/contest/1780

Sasha and the Casino