Educational Codeforces Round 65 (Rated for Div. 2)

7 problems from Educational Codeforces Round 65 (Rated for Div. 2) (contest 1167), difficulty 800-3100. 3/7 solutions verified against sample I/O.

7 items

Educational Codeforces Round 65 (Rated for Div. 2)

Div. 2 | 7 problems | 3/7 verified | Difficulty 800-3100 | 13m 57s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Telephone Number	800	brute-force, greedy, strings	20,276	2m 3s	✓
B	Lost Numbers	1400	brute-force, divide-and-conquer, interactive	16,459	1m 25s
C	News Distribution	1400	dfs-and-similar, dsu, graphs	25,981	3m 18s	✓
D	Bicolored RBS	1500	constructive-algorithms, greedy	7,369	2m 39s	✓
E	Range Deleting	2100	binary-search, combinatorics, data-structures	2,924	1m 35s
F	Scalar Queries	2300	combinatorics, data-structures, math	1,890	1m 24s
G	Low Budget Inception	3100	brute-force, geometry	166	1m 33s

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CF 1167G - Low Budget Inception

The city is a sequence of unit square buildings placed along an infinite horizontal line. Each building occupies an interval of length one, starting at some integer coordinate $ai$. So building $i$ spans $[ai, ai + 1]$, and these positions are strictly increasing.

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CF 1167E - Range Deleting

We are given an array where every element lies between 1 and x, and we consider a transformation defined by a value interval [l, r]. This transformation deletes every array element whose value falls inside that interval, while leaving all other elements in their original order.

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CF 1167B - Lost Numbers

We are given an unknown ordering of six fixed numbers: 4, 8, 15, 16, 23, and 42. Each number appears exactly once in an array of length six, but their positions are hidden.

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CF 1167F - Scalar Queries

We are given an array of distinct numbers, and we look at every possible contiguous subarray. For each subarray, we temporarily reorder its elements in increasing order, then assign weights based on position in that sorted subarray: the smallest element gets weight 1, the next…

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CF 1167D - Bicolored RBS

We are given a valid parentheses string. Think of it as a walk that starts at height 0, where every opening bracket increases the height by 1 and every closing bracket decreases it by 1, and the walk never goes negative and ends at 0.

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CF 1167A - Telephone Number

We are given a string of digits and we are allowed to delete characters freely, without changing the relative order of the remaining digits. The task is to decide whether we can extract a subsequence of length exactly 11 that forms a valid telephone number.

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CF 1167C - News Distribution

We are given a social network with n users and m groups of friends. Each group contains a list of users who are mutually friends with each other.