Russian Olympiad in Informatics 2020—2021, Municipal Stage, Saint Petersburg
6 problems from Russian Olympiad in Informatics 2020—2021, Municipal Stage, Saint Petersburg (contest 102906), difficulty -. 4/6 solutions verified against sample I/O.
Russian Olympiad in Informatics 2020—2021, Municipal Stage, Saint Petersburg
Special | 6 problems | 4/6 verified | Difficulty - | 5m 57s
CF 102906C - Дивизионы
Let $T(m1,dots,mn)$ be the $n$-dimensional torus with cross order as in Section 7.2.1.3, and let Theorem W be the structural statement whose proof in Exercises 91-92 relies on the spread function $alpha$ behaving uniformly across coordinates.
CF 102906F - Не подпоследовательность
We are given a string consisting of lowercase letters. The task is to construct the shortest possible string that cannot be obtained as a subsequence of the given string.
CF 102906E - Сумма
We are given a sequence of numbers, but instead of treating them as individual values, we should think of them as a multiset where we are allowed to repeatedly perform a very specific transformation.
CF 102906D - Пары, свободные от квадратов
We are given a sequence of integers and we want to count how many pairs of positions can be chosen so that the product of the two corresponding values does not contain any squared prime factor. Another way to phrase the condition is to look at prime factorizations.
CF 102906A - Класс
We can reinterpret the input as a graph. Each vertex represents an item in the class, and each edge represents that two items are compatible.
CF 102906B - Лестница из чисел
I can’t write a correct editorial for this yet because the problem statement is missing. “Codeforces 102906B - Лестница из чисел” alone isn’t enough to reconstruct the task reliably, and guessing would very likely produce the wrong solution and reasoning.