Educational Codeforces Round 181 (Rated for Div. 2)

6 problems from Educational Codeforces Round 181 (Rated for Div. 2) (contest 2125), difficulty 800-3000. 3/6 solutions verified against sample I/O.

6 items

Educational Codeforces Round 181 (Rated for Div. 2)

Div. 2 | 6 problems | 3/6 verified | Difficulty 800-3000 | 10m 7s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Difficult Contest	800	constructive-algorithms, implementation, sortings	27,965	2m 4s
B	Left and Down	900	math, number-theory	27,348	1m 20s	✓
C	Count Good Numbers	1100	bitmasks, combinatorics, math	22,742	2m	✓
D	Segments Covering	1600	dp, math, probabilities	9,270	1m 40s	✓
E	Sets of Complementary Sums	2500	brute-force, combinatorics, dp	1,416	1m 30s
F	Timofey and Docker	3000	binary-search, divide-and-conquer, dp	397	1m 33s

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CF 2125F - Timofey and Docker

Timofey has written a text s and wants to present it to a conference audience. Each attendee understands the topic if the number of times the substring "docker" appears consecutively in s falls within their personal interval [li, ri].

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CF 2125E - Sets of Complementary Sums

The problem asks us to count sets of integers that can be generated as complementary sums from some array of positive integers.

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CF 2125D - Segments Covering

We are working with a line of $m$ cells. Each cell must end up being covered by exactly one chosen interval. There are $n$ candidate segments. Each segment $i$ covers a contiguous range $[li, ri]$, but it is not guaranteed to exist.

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CF 2125A - Difficult Contest

We are given several strings consisting of uppercase letters. Each letter represents a contest problem. A contest is considered difficult if the string contains either "FFT" or "NTT" as a contiguous substring. We may rearrange the letters of the string in any order.

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CF 2125C - Count Good Numbers

A number is called good if none of the primes in its prime factorization are single digit primes. The only single digit primes are 2, 3, 5, and 7, so a number is good exactly when it is not divisible by any of these four primes.

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CF 2125B - Left and Down

We start with a robot placed at a coordinate $(a,b)$ on an infinite grid, and we want to move it back to the origin $(0,0)$.