Educational Codeforces Round 137 (Rated for Div. 2)

Solutions for Educational Codeforces Round 137 (Rated for Div. 2) (contest 1743). 2/7 problems verified against sample I/O. Difficulty range: 800-3000.

7 items

Educational Codeforces Round 137 (Rated for Div. 2)

Type: Div. 2 | Problems: 7 | Verified: 2/7 | Rating range: 800-3000 | Time: 17m 43s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Password	800	brute-force, combinatorics, implementation	2m 46s	✓
B	Permutation Value	800	constructive-algorithms, greedy	2m 23s	✗
C	Save the Magazines	1100	constructive-algorithms, dp, greedy	2m 18s	✓
D	Problem with Random Tests	1700	brute-force, dp, greedy	3m 58s	✗
E	FTL	2400	binary-search, dp	2m 9s	✗
F	Intersection and Union	2300	data-structures, dp, matrices	1m 37s	✗
G	Antifibonacci Cut	3000	bitmasks, combinatorics, constructive-algorithms	2m 32s	✗

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CF 1743D - Problem with Random Tests

We are given a binary string. We may choose any two substrings of that string, convert each substring into the integer represented by its binary notation, and take the bitwise OR of those two integers.

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CF 1743G - Antifibonacci Cut

This problem is Type A. The task is to determine for which numbers of kittens the hostess can achieve equal feeding. The requirement is to give a complete answer for $n=2,3,4$, with proof or construction in each case. The proposed solution attempts exactly this.

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CF 1743E - FTL

We are controlling a ship with two independent weapons. Each weapon has a fixed power and a fixed cooldown time. Once a weapon fires, it becomes unavailable for its cooldown duration, then becomes ready again.

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CF 1743F - Intersection and Union

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CF 1743A - Password

Monocarp's password problem is a counting problem constrained by both digit multiplicities and exclusions. The password is a sequence of four digits. Each sequence must contain exactly two distinct digits, and each of these digits appears exactly twice.

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CF 1743B - Permutation Value

The solution correctly identifies that the sawtooth function $(u) = u - lfloor u rfloor$ captures the fractional part of $x/y$ and that multiplying it by $y$ gives the remainder when $x$ is divided by $y$.

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CF 1743C - Save the Magazines

We have a row of boxes. Box i contains a[i] magazines. A binary string tells us which boxes initially have lids. Every lid is attached to a box that initially contains '1'. That lid has only two choices: stay where it is, or move one position to the left.