Good Bye 2025

9 problems from Good Bye 2025 (contest 2178), difficulty 800-3300. 2/9 solutions verified against sample I/O.

9 items

Good Bye 2025

Special | 9 problems | 2/9 verified | Difficulty 800-3300 | 17m 2s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Yes or Yes	800	greedy, strings	25,720	1m 19s	✓
B	Impost or Sus	900	dp, greedy, implementation	21,573	2m 35s
C	First or Second	1200	dp, greedy, implementation	15,683	1m 48s
D	Xmas or Hysteria	1700	constructive-algorithms, greedy, implementation	6,693	1m 41s
E	Flatten or Concatenate	2000	binary-search, divide-and-conquer, interactive	3,684	2m 11s
F	Conquer or of Forest	2200	combinatorics, math, trees	1,823	35s
G	deCH OR Dations	2800	bitmasks, data-structures, dp	593	2m 22s
H	Create or Duplicate	3300	bitmasks, graphs, number-theory	311	2m 55s
I	Numbers or Fireworks	3300	bitmasks, combinatorics, dp	219	1m 36s	✓

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178H - Create or Duplicate

Santa starts with exactly one present of each of three values, $a$, $b$, and $c$. Let the current counts of these present types be $xa$, $xb$, and $xc$. Initially all three counts are equal to $1$. Two operations are available.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178I - Numbers or Fireworks

We are given a set of cities on a Cartesian grid, each at distinct lattice points, and an integer $k$. The task is to compute a certain "explosiveness" measure over all proper subsets of cities.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178G - deCH OR Dations

We are given a circle with $2n$ points labeled from $1$ to $2n$. Santa draws $n$ chords connecting distinct pairs of points. Chords may intersect. For each prefix of chords $1$ through $ell$, we are asked whether the chords are tight-knit.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178E - Flatten or Concatenate

We are asked to determine the maximum element of a hidden array that was generated from an initial array containing a single power-of-two number.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178F - Conquer or of Forest

We are given a rooted tree with vertices numbered from 1 to $n$. Each vertex is colored based on the size of its subtree: if the subtree size is even, the vertex is white; otherwise, it is black.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178D - Xmas or Hysteria

We are given a village of n elves, each with an initial health equal to its attack value. The elves engage in a Mass Hysteria event where each elf that has not attacked yet can choose another living elf to attack.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178B - Impost or Sus

We start with a string consisting only of s and u. We may repeatedly choose any position containing u and change it into s. We are not allowed to change an s back into u. The final string must satisfy two conditions. First, it must contain at least two occurrences of s.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178C - First or Second

We have a line of children, each with an integer niceness value. Santa wants to assign each child to either a nice list or a naughty list, but he can only remove children from the front of the line.

Practice › Codeforces Solutions › Good Bye 2025 ›

CF 2178A - Yes or Yes

We are given a string consisting only of two symbols, where one behaves like a neutral value and the other behaves like an absorbing “true” value under an OR-like merge operation.