Educational Codeforces Round 74 (Rated for Div. 2)

7 problems from Educational Codeforces Round 74 (Rated for Div. 2) (contest 1238), difficulty 900-2700. 3/7 solutions verified against sample I/O.

7 items

Educational Codeforces Round 74 (Rated for Div. 2)

Div. 2 | 7 problems | 3/7 verified | Difficulty 900-2700 | 30m 18s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Prime Subtraction	900	math, number-theory	28,046	1m 23s	✓
B	Kill `Em All	1300	greedy, sortings	14,874	2m 33s
C	Standard Free2play	1600	dp, greedy, math	7,851	6m 2s
D	AB-string	1900	binary-search, combinatorics, dp	6,442	6m 17s
E	Keyboard Purchase	2200	bitmasks, dp	3,460	8m 18s
F	The Maximum Subtree	2200	dfs-and-similar, dp, graphs	2,060	1m 56s	✓
G	Adilbek and the Watering System	2700	data-structures, greedy, sortings	493	3m 49s	✓

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CF 1238E - Keyboard Purchase

We are given a fixed string that we type repeatedly using a one-finger keyboard. The keyboard is defined by choosing a permutation of the first $m$ lowercase letters, and this permutation places each letter at a unique position on a line.

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CF 1238G - Adilbek and the Watering System

The system can only run if it never becomes empty, meaning at every minute it must contain at least one liter before consumption happens. It continuously drains one liter per minute for a total of m minutes, and its storage capacity is capped at c.

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CF 1238D - AB-string

We are given a binary string consisting only of the characters A and B. Our task is to count how many of its contiguous substrings are “good” under a specific structural condition involving palindromes.

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CF 1238C - Standard Free2play

We can think of the cliff as a vertical line of heights from 1 up to h, with a special starting platform at height h. Some of these heights already contain usable platforms, while the rest are empty. You are standing at the top platform and want to reach ground level 0.

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CF 1238B - Kill `Em All

The corridor can be seen as a number line where all monsters start strictly on the positive side. Each monster is a point on this line, and Ivan repeatedly performs an operation that chooses a center point and affects every monster depending on whether it lies to the left, at…

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CF 1238F - The Maximum Subtree

We are given a tree and need to find the largest connected subgraph that can be represented as an intersection graph of line segments on a line.

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CF 1238A - Prime Subtraction

We are given two integers, x and y, with x y. The task is to determine whether it is possible to choose a single prime number p and repeatedly subtract it from x until we reach y. Importantly, once a prime is chosen, it must be used exclusively; we cannot switch primes mid-way.