Hello 2023

Solutions for Hello 2023 (contest 1779). 1/8 problems verified against sample I/O. Difficulty range: 800-3500.

8 items

Hello 2023

Type: Special | Problems: 8 | Verified: 1/8 | Rating range: 800-3500 | Time: 15m 54s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Hall of Fame	800	constructive-algorithms, greedy, strings	1m 53s	✗
B	MKnez's ConstructiveForces Task	900	constructive-algorithms, math	1m 2s	✗
C	Least Prefix Sum	1600	data-structures, greedy	1m 59s	✗
D	Boris and His Amazing Haircut	1700	constructive-algorithms, data-structures, dp	1m 35s	✗
E	Anya's Simultaneous Exhibition	2400	constructive-algorithms, graphs, greedy	3m 24s	✗
F	Xorcerer's Stones	2500	bitmasks, constructive-algorithms, dp	1m 29s	✗
G	The Game of the Century	3000	constructive-algorithms, graphs, shortest-paths	3m 11s	✗
H	Olympic Team Building	3500	brute-force, meet-in-the-middle	1m 21s	✓

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779G - The Game of the Century

The village is represented as a triangular grid of intersections. Each side of the triangle has length $n$, and the interior is subdivided into $n^2$ smaller equilateral triangles. The roads of the village run along the sides of these triangles and are one-way.

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779E - Anya's Simultaneous Exhibition

We are asked to identify candidate masters among a group of chess players where the outcome of any head-to-head match is deterministic but may be non-transitive. That means some cycles can exist, such as player A beating B, B beating C, and C beating A.

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779H - Olympic Team Building

We are given a set of $n$ players, where $n$ is a power of two, and each player has a fixed positive strength. A sequence of elimination rounds is played. In each round, the current set of players is split into two equal groups.

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779F - Xorcerer's Stones

We are given a rooted tree where each node stores a small integer value. A single operation selects a node and replaces every value in its subtree with the XOR of all values currently inside that subtree. After this assignment, every node in that subtree becomes identical.

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779D - Boris and His Amazing Haircut

We are asked to transform Boris's current hairstyle into a desired one using a limited set of razors, each of which can cut hair down to a fixed length over any contiguous segment.

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779C - Least Prefix Sum

We are given an array of integers, and Baltic wants a specific prefix sum-the sum of the first m elements-to be the smallest among all prefix sums of the array. We are allowed to flip the sign of any element any number of times.

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779A - Hall of Fame

Thalia has a line of trophies, each with a lamp that can shine either to the left or to the right. The lamp at position i illuminates all trophies strictly in the direction it points, excluding itself.

Practice › Codeforces Solutions › Hello 2023 ›

CF 1779B - MKnez's ConstructiveForces Task

This is a Type B problem: prove impossibility. The solution correctly identifies that the task is to show that no plane can cut a regular $n$-gonal pyramid into a regular $(n+1)$-gon when $n ge 5$.