Hello 2020

7 problems from Hello 2020 (contest 1284), difficulty 800-3300. 4/7 solutions verified against sample I/O.

7 items

Hello 2020

Special | 7 problems | 4/7 verified | Difficulty 800-3300 | 46m 59s

#	Problem	Rating	Tags	Accepted	Time	✓
A	New Year and Naming	800	implementation, strings	18,594	8m 32s	✓
B	New Year and Ascent Sequence	1400	binary-search, combinatorics, data-structures	11,458	2m 36s	✓
C	New Year and Permutation	1600	combinatorics, math	8,737	2m 1s	✓
D	New Year and Conference	2100	binary-search, data-structures, hashing	3,397	2m 35s	✓
E	New Year and Castle Construction	2500	combinatorics, geometry, math	1,379	7m 49s
F	New Year and Social Network	3200	data-structures, graph-matchings, graphs	413	10m
G	Seollal	3300	graphs	228	13m 26s

Practice › Codeforces Solutions › Hello 2020 ›

CF 1284G - Seollal

The task is to take a small grid with blocked and open cells and construct a special “maze representation” on a refined grid. Each input cell becomes a node in a graph, and adjacency exists between orthogonally neighboring open cells.

Practice › Codeforces Solutions › Hello 2020 ›

CF 1284F - New Year and Social Network

We are given two different spanning trees over the same set of $n$ vertices. One tree, call it $T1$, represents the main network, and the second tree $T2$ is a backup structure. Each edge in $T1$ is a potential failure point.

Practice › Codeforces Solutions › Hello 2020 ›

CF 1284E - New Year and Castle Construction

We are given a set of points in the plane, with the restriction that no three points lie on a single line. For every point (p), we want to count how many subsets of exactly four other points can form a simple quadrilateral that strictly contains (p).

Practice › Codeforces Solutions › Hello 2020 ›

CF 1284A - New Year and Naming

We are given two circular lists of strings. The first list has size $n$, the second has size $m$. Each year $y$ produces a name by taking the $y$-th string from the first list and the $y$-th string from the second list, both indexed cyclically, and concatenating them.

Practice › Codeforces Solutions › Hello 2020 ›

CF 1284B - New Year and Ascent Sequence

We are given a collection of integer sequences, and we consider ordered pairs of them. For any pair of sequences $sx$ and $sy$, we concatenate them to form a longer sequence $sx + sy$.

Practice › Codeforces Solutions › Hello 2020 ›

CF 1284D - New Year and Conference

Each lecture in the conference has two possible time schedules, depending on which venue is chosen. If we pick venue A, every lecture follows its A-interval. If we pick venue B, every lecture follows its B-interval.

Practice › Codeforces Solutions › Hello 2020 ›

CF 1284C - New Year and Permutation

We need the total number of framed segments across all permutations of length n. For a fixed permutation, a segment [l, r] is framed when the values inside it form a set of consecutive integers.