Hello 2026

11 problems from Hello 2026 (contest 2183), difficulty 800-3500. 0/11 solutions verified against sample I/O.

11 items

Hello 2026

Special | 11 problems | 0/11 verified | Difficulty 800-3500 | 23m 31s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Binary Array Game	800	games	23,656	1m 37s
B	Yet Another MEX Problem	1100	constructive-algorithms, greedy	16,159	2m 32s
C	War Strategy	1500	binary-search, greedy, math	10,658	2m 27s
D1	Tree Coloring (Easy Version)	1500	constructive-algorithms, dfs-and-similar, greedy	8,838	2m 31s
D2	Tree Coloring (Hard Version)	2100	combinatorics, constructive-algorithms, data-structures	2,497	1m 58s
E	LCM is Legendary Counting Master	2100	dp, math, number-theory	2,850	2m 10s
F	Jumping Man	2500	brute-force, combinatorics, dfs-and-similar	1,124	2m 24s
G	Snake Instructions	3200	constructive-algorithms, greedy, interactive	221	2m 47s
H	Minimise Cost	3500	binary-search, dp, greedy	159	1m 56s
I1	Pairs Flipping (Easy Version)	3500	constructive-algorithms	82	1m 27s
I2	Pairs Flipping (Hard Version)	3500	constructive-algorithms	69	1m 42s

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183I2 - Pairs Flipping (Hard Version)

We are given a binary string where each position contains either a 0 or a 1. We are allowed a fixed number of operations, exactly one for each value from 1 up to half the length of the string.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183I1 - Pairs Flipping (Easy Version)

We are working with a binary string where each position holds either a 0 or a 1, and we are allowed to repeatedly apply a very specific kind of operation. Each operation is indexed from 1 upward, and on operation number x we may choose a starting position l.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183G - Snake Instructions

The interactive version allows us to ask up to three carefully chosen instructions and observe the surviving snakes. In the hacked version, the speeds are already given in the input, and our job is to reproduce the answer that an optimal interactive solution would output.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183H - Minimise Cost

We are given an array of integers and asked to divide it into exactly $k$ non-empty subsequences. For any subsequence $b$, its cost is defined as the product of its length and the sum of its elements. Our goal is to minimize the total cost across all $k$ subsequences.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183F - Jumping Man

We are given a rooted tree with each node labeled by a lowercase letter. For each node $i$, we are asked to analyze all strings that can be formed by starting at any node in the subtree of $i$ and repeatedly jumping to a proper descendant, concatenating the letters along the…

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183E - LCM is Legendary Counting Master

We are given a sequence of length $n$ where some positions are fixed numbers between $1$ and $m$, and some positions are zero placeholders that must be filled. After filling all zeros with values in $[1, m]$, the resulting sequence must satisfy two conditions at the same time.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183D2 - Tree Coloring (Hard Version)

We are given a rooted tree, where all nodes are initially white, and we need to color all nodes black in the minimum number of operations.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183D1 - Tree Coloring (Easy Version)

We are given a rooted tree with n vertices, where the root is vertex 1, and initially all vertices are white. The distance di of a vertex i is the number of edges on the path from the root to i.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183B - Yet Another MEX Problem

We are given an array of non-negative integers and a number $k$. The task is to repeatedly remove elements from the array, always choosing a window of length $k$ whose MEX is maximal, and deleting any element within that window.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183C - War Strategy

We have a linear arrangement of bases numbered from 1 to n. Our home base is at position k, and we start with exactly one soldier there. Every day, we can select a base and move any number of soldiers from it either left or right by exactly one position.

Practice › Codeforces Solutions › Hello 2026 ›

CF 2183A - Binary Array Game

We are given a binary array that evolves through a merging game. Two players, Alice and Bob, alternate turns. On each turn, a player selects a contiguous segment of length at least two, removes it, and replaces it with a single value derived from that segment.