CodeTON Round 3 (Div. 1 + Div. 2, Rated, Prizes!)

Solutions for CodeTON Round 3 (Div. 1 + Div. 2, Rated, Prizes!) (contest 1750). 4/8 problems verified against sample I/O. Difficulty range: 800-3500.

8 items

CodeTON Round 3 (Div. 1 + Div. 2, Rated, Prizes!)

Type: Div. 1+2 | Problems: 8 | Verified: 4/8 | Rating range: 800-3500 | Time: 24m 36s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Indirect Sort	800	constructive-algorithms, implementation, math	2m 1s	✓
B	Maximum Substring	800	brute-force, greedy, implementation	6m 45s	✓
C	Complementary XOR	1400	constructive-algorithms, implementation	7m 11s	✗
D	Count GCD	1800	combinatorics, math, number-theory	1m 20s	✓
E	Bracket Cost	2400	binary-search, data-structures, divide-and-conquer	2m 15s	✗
F	Majority	2700	combinatorics, dp, math	2m 10s	✓
G	Doping	3300	combinatorics, dp, math	1m 11s	✗
H	BinaryStringForces	3500	constructive-algorithms, data-structures, dp	1m 43s	✗

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CF 1750H - BinaryStringForces

I can't reliably write a correct editorial for Codeforces 1750H from the statement alone. This is a 3500-rated problem, and producing a full editorial with proof, algorithm, complexity analysis, worked examples, and code requires knowing the actual accepted solution.

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CF 1750G - Doping

Codeforces 1750G: Doping

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CF 1750F - Majority

We are asked to count how many binary strings of length $n$ can be fully turned on using a special operation called "electricity spread." Each string represents a line of servers, where 1 means the server is online and 0 means it is offline.

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CF 1750C - Complementary XOR

We are given two binary strings of equal length. A single operation chooses a segment ([l,r]). Every bit of string (a) inside the segment is flipped, while every bit of string (b) outside the segment is flipped. The goal is not to transform one string into the other.

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CF 1750B - Maximum Substring

We are given a binary string and asked to examine every contiguous segment. For each segment we count how many zeros and ones it contains, and then assign it a score based on those counts. If both symbols appear, the score is the product of the two counts.

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CF 1750E - Bracket Cost

We are given a binary string made of parentheses, and we examine every contiguous segment of it independently. For each segment, we are allowed to transform it into a correct bracket sequence using two operations: we can insert single parentheses anywhere, and we can take any…

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CF 1750D - Count GCD

We are asked to count arrays $b$ that match a sequence of prefix greatest common divisors. Concretely, for each position $i$, the GCD of the first $i$ elements of $b$ must equal $ai$. Each element $bi$ must be an integer between 1 and $m$.

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CF 1750A - Indirect Sort

We are given a small permutation, meaning every number from 1 to n appears exactly once. The task is to determine whether we can transform this array into sorted order using a very specific operation that involves three indices i < j < k.