Codeforces Global Round 15

9 problems from Codeforces Global Round 15 (contest 1552), difficulty 800-3400. 4/9 solutions verified against sample I/O.

9 items

Codeforces Global Round 15

Global | 9 problems | 4/9 verified | Difficulty 800-3400 | 40m 13s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Subsequence Permutation	800	sortings, strings	25,328	6m 22s	✓
B	Running for Gold	1500	combinatorics, graphs, greedy	16,929	1m 43s	✓
C	Maximize the Intersections	1800	combinatorics, constructive-algorithms, geometry	6,286	7m 19s
D	Array Differentiation	1800	bitmasks, brute-force, constructive-algorithms	7,886	5m 22s
E	Colors and Intervals	2300	constructive-algorithms, data-structures, greedy	2,125	7m 14s
F	Telepanting	2200	binary-search, data-structures, dp	3,333	5m 13s
G	A Serious Referee	3000	bitmasks, brute-force, dfs-and-similar	670	1m 14s
H	Guess the Perimeter	3300	binary-search, interactive, number-theory	462	3m 43s	✓
I	Organizing a Music Festival	3400	dfs-and-similar, math	147	2m 3s	✓

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CF 1552D - Array Differentiation

We are given a list of integers, and we want to decide whether it is possible to assign another list of the same length, say $b1, b2, dots, bn$, such that every given number $ai$ can be expressed as a difference between two values in $b$.

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CF 1552I - Organizing a Music Festival

We are asked to count how many permutations of singers are valid under a set of “group contiguity” constraints. Each singer is a distinct element from $1$ to $n$. We must arrange all of them in a line.

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CF 1552H - Guess the Perimeter

We are dealing with a hidden axis-aligned rectangle whose corners lie on integer grid points inside a fixed 200 by 200 grid.

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CF 1552C - Maximize the Intersections

We are given points placed around a circle in clockwise order. Some of these points are already connected by chords, and these initial chords never share endpoints.

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CF 1552E - Colors and Intervals

We are given a long line of positions from 1 to n·k, each position painted with one of n colors, and each color appears exactly k times. For every color i we must choose exactly one interval [ai, bi] such that both endpoints belong to positions colored i.

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CF 1552F - Telepanting

We are simulating a point moving on a number line. The point starts at position 0 and moves strictly to the right at unit speed, so without any interruptions it would simply take $t$ seconds to reach position $t$.

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CF 1552A - Subsequence Permutation

We are given a string made of lowercase letters. In one move, we are allowed to pick exactly one subset of positions, take the characters at those positions, and rearrange only those chosen characters arbitrarily while keeping all other characters fixed in their original places.

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CF 1552G - A Serious Referee

We are asked to determine if a specific sequence of partial sorts can guarantee that any array of length $n$ will be fully sorted at the end. The input specifies $n$, the size of the array, and $k$, the number of sorting steps Andrea performs.

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CF 1552B - Running for Gold

Each athlete is described by five rankings, one ranking from each past marathon. Smaller values are better because a rank of 1 means first place. For two athletes x and y, we say that x is superior to y if x has a better rank in at least three of the five marathons.