What problems do the problems of Educational Codeforces Round 147 remind you of?

#1

As the question title suggests, what specific past problems do the problems of the recent Educational Codeforces Round 147 remind you of?

I think this is of interest especially to newer contestants looking for extra practice, also maybe others as well.

Here are the problems for Educational Codeforces Round 147: Dashboard - Educational Codeforces Round 147 (Rated for Div. 2) - Codeforces

And here’s the editorial: Educational Codeforces Round 147 — Editorial - Codeforces