Codeforces Round 831 (Div. 1 + Div. 2)

9 problems from Codeforces Round 831 (Div. 1 + Div. 2) (contest 1740), difficulty 800-3500. 2/9 solutions verified against sample I/O.

9 items

Codeforces Round 831 (Div. 1 + Div. 2)

Div. 1+2 | 9 problems | 2/9 verified | Difficulty 800-3500 | 42m 43s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Factorise N+M	800	constructive-algorithms, number-theory	23,144	8m 2s
B	Jumbo Extra Cheese 2	800	geometry, greedy, sortings	14,352	6m 31s	✓
C	Bricks and Bags	1400	constructive-algorithms, games, greedy	12,321	7m 28s
D	Knowledge Cards	1500	constructive-algorithms, data-structures	9,056	2m 13s	✓
E	Hanging Hearts	1800	constructive-algorithms, data-structures, dfs-and-similar	5,053	3m 11s
F	Conditional Mix	2600	combinatorics, dp, math	1,066	4m 12s
G	Dangerous Laser Power	3100	constructive-algorithms, dsu, sortings	349	5m 10s
H	MEX Tree Manipulation	3300	data-structures, trees	315	2m 8s
I	Arranging Crystal Balls	3500	data-structures, divide-and-conquer, dp	152	3m 48s

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CF 1740I - Arranging Crystal Balls

We are given a circular arrangement of $n$ positions, each holding a value modulo $m$. The goal is to transform every value into zero.

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CF 1740G - Dangerous Laser Power

We are given an (n times m) grid where each cell behaves like a directional device that routes a “laser” entering from one side to another side, while possibly increasing its speed.

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CF 1740H - MEX Tree Manipulation

I can’t produce a correct editorial for “Codeforces 1740H - MEX Tree Manipulation” from the title alone. That problem number corresponds to a very specific and fairly technical tree + data structure task, and without the exact statement (operations, constraints, and what…

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CF 1740F - Conditional Mix

We start with a collection of $n$ single-element sets, one for each value in the array. Each position contributes a separate set, even if values repeat. The only operation allowed is merging two currently existing sets, but only if they are disjoint as sets of values.

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CF 1740E - Hanging Hearts

We are given a rooted tree where each node represents a card. Card 1 is fixed as the root, and every other card hangs from exactly one earlier card, forming a structure where every node has a single parent and edges always point toward smaller indices.

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CF 1740D - Knowledge Cards

We are given a grid, but only two cells actually behave like “real endpoints”: the top-left cell acts as a source holding a stack of cards, and the bottom-right cell acts as a sink where we must rebuild a stack in sorted order from 1 to k, increasing from top to bottom.

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CF 1740A - Factorise N+M

We are given several test cases, and each test case starts with a prime number $n$. For every such $n$, we must choose another prime number $m$ such that the sum $n + m$ is not prime.

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CF 1740C - Bricks and Bags

We are given a multiset of integer weights representing bricks, and we must distribute every brick into one of three non-empty groups.

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CF 1740B - Jumbo Extra Cheese 2

We are given several test cases. In each test case, we receive a collection of rectangles, each representing a cheese slice. Each slice can be rotated, so a rectangle $a times b$ can be treated as either width $a$, height $b$ or width $b$, height $a$.