Codeforces Global Round 11

Solutions for Codeforces Global Round 11 (contest 1427). 3/8 problems verified against sample I/O. Difficulty range: 900-3500.

8 items

Codeforces Global Round 11

Type: Global | Problems: 8 | Verified: 3/8 | Rating range: 900-3500 | Time: 20m 47s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Avoiding Zero	900	math, sortings	9m 6s	✗
B	Chess Cheater	1400	greedy, implementation, sortings	2m	✗
C	The Hard Work of Paparazzi	2000	dp	1m 45s	✓
D	Unshuffling a Deck	2000	constructive-algorithms, implementation	1m 47s	✓
E	Xum	2500	bitmasks, constructive-algorithms, math	1m 34s	✓
F	Boring Card Game	3200	data-structures, greedy, trees	1m 23s	✗
G	One Billion Shades of Grey	3300	flows, graphs	1m 40s	✗
H	Prison Break	3500	binary-search, games, geometry	1m 32s	✗

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CF 1427A - Avoiding Zero

We are given an array of integers and the task is to reorder its elements so that no prefix sum of the resulting array is zero. The array can contain positive, negative, and zero values, and we must maintain the multiset of original values.

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CF 1427H - Prison Break

We are asked to compute the minimum speed $v$ at which two guards can prevent a prisoner from escaping a convex polygonal prison. The prisoner starts outside the main perimeter on a fixed point far to the left.

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CF 1427G - One Billion Shades of Grey

We are given an $n times n$ grid representing a wall made of tiles. Some tiles are already painted with a shade of grey (an integer from 1 to $10^9$), some are broken and cannot be painted (marked as $-1$), and the rest are unpainted (marked as 0).

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CF 1427F - Boring Card Game

We are given a deck of 6n cards numbered consecutively from 1 to 6n. Two players, Federico and Giada, alternately take turns picking exactly three consecutive cards from the remaining deck. Federico starts, and after all 2n turns, each player has exactly 3n cards.

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CF 1427E - Xum

We start from a single odd integer placed on a board. From there, we are allowed to repeatedly create new numbers by either adding two already available numbers or taking their bitwise XOR.

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CF 1427D - Unshuffling a Deck

We are given a deck of n cards, each labeled with a unique integer from 1 to n, in an arbitrary order. The goal is to sort the deck into ascending order using a special operation.

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CF 1427B - Chess Cheater

We are given the results of a series of chess games as a string consisting of 'W' for wins and 'L' for losses. Each win grants points depending on whether it continues a streak of previous wins: the first win or a win following a loss gives 1 point, while a win immediately…

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CF 1427C - The Hard Work of Paparazzi

The task is to maximize the number of celebrities a paparazzi can photograph in a city represented as an (r times r) grid of streets. Each celebrity will appear at a specific intersection ((xi, yi)) at a specific time (ti), and the paparazzi starts at ((1, 1)).