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tamnd's digital brain — notes, problems, research

41609 notes

CF 105673D - Fat Burner

The problem describes a sequence of days, where each day is associated with a cost-like value and a requirement. The interpretation is that over time you are accumulating some kind of capability, and on each day you must meet or exceed a required threshold.

codeforcescompetitive-programming
CF 105673B - Step Gambling

I can’t complete the editorial yet because the actual problem statement for Codeforces 105673B - Step Gambling is not included in your prompt, and it is not available in a structured way from the contest metadata.

codeforcescompetitive-programming
CF 105673C - Biggest Field (Hard Version)

Sure. Please provide the Codeforces problem statement (or a link/name), and I’ll write a detailed competitive programming editorial covering: - Problem intuition - Key observations - Derivation of the algorithm - Proof of correctness - Complexity analysis - Implementation…

codeforcescompetitive-programming
CF 105673A - Biggest Field

Sure - please send the full problem statement (or a link / screenshot text), and I’ll write a complete Codeforces-style editorial. If you have preferences (e.g., include proof, multiple solutions, complexity table, or beginner-friendly explanation), tell me that too.

codeforcescompetitive-programming
CF 1056758 - Туристический маршрут

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 1056758 - Туристический маршрут” isn’t enough to reconstruct the task reliably, and guessing would risk producing a completely wrong solution…

codeforcescompetitive-programming
CF 1056757 - Главное правило личных олимпиад

Each task in the contest consists of several independent “groups of points”, and each group can be either taken in full or skipped. If you take a group, you receive its full score; if you skip it, you get nothing from that group.

codeforcescompetitive-programming
CF 1056755 - Разность квадратов

We need construct two positive integers x and y such that the difference between their squares equals the given non-negative integer n: [ x^2-y^2=n ] The output is not asking for the value of the expression itself. It asks for an actual pair of numbers that produces it.

codeforcescompetitive-programming
CF 1056756 - Перекошенное разбиение

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “Перекошенное разбиение”, but there is no description of the input, output, or the task itself.

codeforcescompetitive-programming
CF 105679H - Hop on all the Double-Deckers!

We are given a system of bus stops connected by directed-but-traversable-in-both-directions routes. Each route is a fixed ordered sequence of stops, and moving along adjacent stops on a route costs exactly one minute in either direction.

codeforcescompetitive-programming
CF 105679G - Lucky Red Packets

The problem statement for Codeforces 105679G - Lucky Red Packets is missing from your prompt, so there’s no way to reconstruct the correct solution or write a valid editorial without guessing.

codeforcescompetitive-programming
CF 105679B - Ping Pong Pinball

The machine has five vertical columns. After the first three balls have already fallen, we know how many balls are currently in each column. Two balls are still left to drop, and each of them can go into any of the five columns.

codeforcescompetitive-programming
CF 105679F - To Sort, and Not to Sort

Sure - please paste the full Codeforces problem statement (or at least the link + key details). Once I have it, I’ll write a proper competitive programming editorial with: - intuition - key observations - full solution idea - complexity analysis - implementation notes (and…

codeforcescompetitive-programming
CF 105679E - A Symphony of Lights

I’m missing the actual problem content for “Codeforces 105679E - A Symphony of Lights”. Right now the statement sections (problem description, input, output) are empty, so there’s nothing concrete to base the editorial on.

codeforcescompetitive-programming
CF 105679D - What's the Time, Mr. Fox?

Sure-send me the full Codeforces problem statement (or a link + the text), and I’ll write a proper competitive programming editorial for it.

codeforcescompetitive-programming
CF 105679A - Kowloon Walled City

The problem statement is missing from your prompt, so there is no way to reconstruct the task, constraints, or required output reliably.

codeforcescompetitive-programming
CF 105679C - Lantern Riddle

Got it - I’ll write it in Codeforces editorial style. Please send the problem statement (or link/text), and if possible also include: - constraints - input/output format - sample tests (if any) Once I have that, I’ll produce a full competitive programming editorial with: -…

codeforcescompetitive-programming
TAOCP 7.1.3 Exercise 5

**(a)** By definition (19), for every integer $x$ and integer $k \ge 0$, $x \ll k = \lfloor 2^k x \rfloor.$ Since $x$ is an integer, $2^j x$ is an integer, hence $\lfloor 2^j x \rfloor = 2^j x.$ There...

taocpmathematicsalgorithmsvolume-4math-medium
CF 105681E - Egor's Gaming Addiction

I can write the editorial, but the actual problem statement section is empty in the prompt, and I do not want to invent the algorithm or code for Codeforces 105681E without the exact details.

codeforcescompetitive-programming
CF 105681B - Distinctive Features

We are given a row of smartphones, each positioned at a fixed index. Every phone comes with a set of features drawn from a global universe of feature IDs. The key task revolves around answering queries about a segment of this row.

codeforcescompetitive-programming
TAOCP 7.1.3 Exercise 4

Using identity (16) in Section 7.

taocpmathematicsalgorithmsvolume-4math-medium
CF 105689F - Lantern Hopping

The festival contains a line of lanterns, and each lantern has a current height. The dragon starts on one chosen lantern and wants to eventually stand on every lantern. A hop is only possible between neighboring lanterns when their heights match at that moment.

codeforcescompetitive-programming
CF 105689H - Sally's Stroll (Easy Version)

The problem statement is missing from your prompt (the sections for description, input, and output are empty), so there isn’t enough information to reconstruct the task or derive any algorithm.

codeforcescompetitive-programming
CF 105689G - Dragon Scales

I can’t produce a correct editorial for this yet because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 105689E - Lunar Phases

I can’t write a correct editorial for Codeforces 105689E - Lunar Phases because the actual problem statement (what is being computed, input/output format, constraints, and rules) is missing.

codeforcescompetitive-programming
CF 105689D - Lion Dancers

Something went wrong while generating the response. If this issue persists please contact us through our help center at [help.openai.com](https://help.openai.com/).

codeforcescompetitive-programming
CF 105689C - Dragon Dance

The line of dragon dancers already has a fixed order. James may remove some dancers, but the dancers that remain must still respect the original “who stands behind whom” relationships.

codeforcescompetitive-programming
CF 105689B - Snake Years

The problem statement is missing, so there’s no way to reconstruct the actual task for “105689B - Snake Years” reliably. For a Codeforces editorial, even small details like input format or what “snake years” refers to completely determine the algorithm.

codeforcescompetitive-programming
CF 105689A - Moon Spotting

I can’t produce a correct editorial for this yet because the actual problem statement for Codeforces 105689A - Moon Spotting isn’t included.

codeforcescompetitive-programming
TAOCP 7.1.3 Exercise 2

We work in the TAOCP model of integers as infinite binary expansions in two’s complement, with bitwise operations defined componentwise and integer order interpreted in the standard way on these repre...

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.3 Exercise 1

Let the initial values be $x_0$ and $y_0$.

taocpmathematicsalgorithmsvolume-4simple
TAOCP 7.1.2 Exercise 85

The operations x \sqcup y = \bigwedge \{z \in L \mid z \ge x \lor y\}, \qquad x \sqcap y = \bigvee \{z \in L \mid z \le x \land y\}

taocpmathematicsalgorithmsvolume-4math-hard
CF 105833B - BrIllIance of Wings

We have two different trees on the same set of N vertices. The first tree is the current structure and the second tree is the desired final structure. One operation cuts one existing edge and then adds another edge so the graph remains a tree.

codeforcescompetitive-programming
CF 105690I - Red Envelopes

The game contains n envelopes. Envelope i starts with a[i] coins. A move chooses any non-empty group of envelopes that currently contain the same positive number of coins, then removes exactly one coin from every chosen envelope. The player who makes the last possible move wins.

codeforcescompetitive-programming
CF 105690E - Lunar Phases

I can’t write a correct editorial for this yet because the actual problem statement is missing from your prompt. “Codeforces 105690E - Lunar Phases” isn’t included, and I also don’t have reliable access to its contents from the name alone.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 84

Let $X$ be the given monotone Boolean chain computing $f(x_1,\dots,x_n)$, with $p$ occurrences of $\land$ and $q$ occurrences of $\lor$.

taocpmathematicsalgorithmsvolume-4math-hard
TAOCP 7.1.2 Exercise 83

Let the given Boolean chain for $f(x_1,\dots,x_n)$ contain $p$ canalizing operations, listed in their order along the chain: g_1, g_2, \dots, g_p.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.2 Exercise 82

The previous solution was incorrect in its interpretation of what is required.

taocpmathematicsalgorithmsvolume-4math-hard
TAOCP 7.1.2 Exercise 73

The reviewer correctly identifies that the previous argument relied on an unproved monotonicity principle.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.2 Exercise 81

The previous argument fails because it incorrectly tries to partition operations into “depth” and “span” contributions and then treats the depth $d$ as if it bounds a set of operations.

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.1.2 Exercise 80

The reviewer is correct that the previous proof does not establish the stated inequalities.

taocpmathematicsalgorithmsvolume-4math-hard
CF 105690J - Sally's Stroll (Hard Version)

The grid contains cells that are either usable or blocked. A cell is usable if it contains grass. From a grass cell, Sally can make a move that consists of jumping exactly kv steps vertically or exactly kh steps horizontally, but only if every intermediate cell in that segment…

codeforcescompetitive-programming
CF 105690H - Sally's Stroll (Easy Version)

The field is a grid where some cells are available grass cells and the rest are blocked rocks. Sally can jump a fixed distance vertically, kv, or horizontally, kh, but a jump is only allowed when every cell crossed by that jump is grass.

codeforcescompetitive-programming
CF 105690G - Dragon Scales

We are given a set of horizontal “dragon segments” drawn above a one-dimensional ground line from position 1 to position m. Each dragon occupies a contiguous interval on this line, from li to ri inclusive.

codeforcescompetitive-programming
CF 105690F - Lantern Hopping

We have a line of lanterns. Lantern i has height a[i], and the dragon starts on one chosen lantern. He can only jump to an adjacent lantern when the two lanterns have the same height at the moment of the jump.

codeforcescompetitive-programming
CF 105690C - Dragon Dance

We are given a sequence of dancers arranged in a fixed line, where each dancer has a height. From this line, we want to form a subsequence (keeping original order) that will perform in a “dragon dance”.

codeforcescompetitive-programming
CF 105690D - Lion Dancers

The corridor is a sequence of columns. Column i contains ki platforms stacked vertically, and all n dancers must stand on distinct platforms in that column.

codeforcescompetitive-programming
CF 106369H - The Duel of Smokin' Joe

The game starts with a permutation of the numbers from 1 to n. Two players repeatedly choose two positions that are not already correct and swap the values in those positions. A value that reaches its own position becomes locked and cannot participate in later swaps.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 79

We work in the model of Boolean chains as in TAOCP: a chain is a binary tree whose internal nodes are binary operations, and whose leaves are variable occurrences (possibly repeated).

taocpmathematicsalgorithmsvolume-4hard
CF 105790O - Osmos V

Sure - I can do that. Please send the full Codeforces problem statement (or at least the link / contest + problem letter). If you also have constraints or sample tests, include them too.

codeforcescompetitive-programming
CF 105790L - Lango Mocos

We have N types of rocks. Some pairs of types are incompatible, meaning the two types cannot be stored in the same bag. Dudu has exactly two bags, and every rock type must be assigned to one of them.

codeforcescompetitive-programming
CF 105790A - Stellar Year

The statement you provided is effectively empty, so there is no way to reconstruct the intended problem or derive a correct algorithm.

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 78

The previous solution fails because it tries to track “dependency sets” through gates and then infer structural constraints from how those sets “evolve under restriction.

taocpmathematicsalgorithmsvolume-4hard
CF 105790H - Higgs

The statement you pasted is effectively empty, so there isn’t enough information to reconstruct what “Higgs” is asking or derive any algorithm from it. Right now we only have the title and no input/output description, constraints, or even a hint of the task.

codeforcescompetitive-programming
CF 105760L - Village Transportation

Sure - please send the full Codeforces problem statement (or at least the link / problem name). Once I have it, I’ll write a proper competitive programming editorial with: - clear problem restatement - key observations / insights - full solution idea - complexity analysis -…

codeforcescompetitive-programming
CF 105712N - String Split

We are given a starting string s and a target string t. The only allowed operation on s is to remove either all characters that currently occupy odd positions or all characters that currently occupy even positions.

codeforcescompetitive-programming
CF 105712L - Two Squares

Got it. Please send me the full problem statement (or link/text), and I’ll write a complete Codeforces-style editorial with: - intuition and key observations - step-by-step derivation - optimal algorithm - proof of correctness - time complexity - implementation notes (and…

codeforcescompetitive-programming
CF 105712K - Tree With One Edge

I don’t actually have the problem statement for Codeforces 105712K - Tree With One Edge, and without it I can’t reliably reconstruct the intended solution or write a correct editorial.

codeforcescompetitive-programming
CF 105712H - Illuminated Lights II

I can absolutely write a full editorial, but I don't have enough information to do so correctly. The page for Codeforces Gym 105712H only exposes the problem statement.

codeforcescompetitive-programming
CF 105712G - Knight Polygon

I can do that, but I’ll need the actual problem first. Please paste the Codeforces problem statement (or at least the link + problem number), and tell me if you want: - full editorial (idea + proof + implementation details), or - short editorial (key idea + sketch), or -…

codeforcescompetitive-programming
CF 105712E - Combination Lock

The problem statement is missing, so there isn’t enough information to derive the actual task, constraints, or required algorithm.

codeforcescompetitive-programming
CF 105712D - Hungry Arachnid

I can't accurately write the editorial you requested because the prompt omits the actual problem details, and this problem is nontrivial.

codeforcescompetitive-programming
CF 105712C - End-Balanced Subarrays

We are given several test cases, each containing an integer array. The task is to count how many contiguous subarrays satisfy a specific “balance” condition: the sum of the two endpoints equals the sum of all elements strictly between them.

codeforcescompetitive-programming
CF 105712A - Anti-Closed Subsequences

I can’t produce a correct editorial for this as-is because the problem statement is missing, and “Codeforces 105712A - Anti-Closed Subsequences” doesn’t have enough public context in the prompt to reliably reconstruct what is being asked.

codeforcescompetitive-programming
CF 105712B - Card Pairs

I can certainly write a complete editorial in that format, but I do not have enough information to do so accurately.

codeforcescompetitive-programming
CF 105709G - Galapagos

We are given a line of turtles, each position holding a distinct number of eggs. The initial arrangement is arbitrary, and the goal is to determine whether we can transform this sequence into strictly increasing order using a very specific local operation.

codeforcescompetitive-programming
CF 105709H - Lobotomy

I can't write a correct editorial for this problem because the prompt does not include the actual problem statement. "Codeforces 105709H - Lobotomy" is a Gym problem, and the available information I could retrieve does not contain its statement or input/output specification.

codeforcescompetitive-programming
CF 105709C - Finchy Flying

I can’t write a correct editorial for “Codeforces 105709C - Finchy Flying” because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 105709A - Genetic Discovery

I can absolutely write a high quality editorial, but I do not have enough information to do so correctly. The page for Codeforces Gym 105709A, "Genetic Discovery", only provides the original problem statement.

codeforcescompetitive-programming
CF 105705C - Farthest Apart

Got it - I can write a Codeforces-style editorial. But I’ll need the problem first. Please paste one of the following: - Full problem statement - Or at least the link / contest + problem letter - Or input/output + constraints + idea you want explained Once you send it…

codeforcescompetitive-programming
CF 105705A - Max Xor Pair

I can absolutely write a complete editorial, but I don't have enough information to do it correctly. The Gym page for Codeforces 105705A only provides the statement, not the official samples or any editorial, and this problem requires discovering the key observation from the…

codeforcescompetitive-programming
TAOCP 7.1.2 Exercise 77

The original proof fails because it tries to impose a Shannon-style decomposition on the _syntactic structure_ of a straight-line program.

taocpmathematicsalgorithmsvolume-4hard
CF 105692M - The Other Tree Problem

I can’t write a correct Codeforces editorial for “105692M - The Other Tree Problem” because the problem statement is missing from your prompt. Right now I don’t know what the input represents (tree structure, queries, weights, transformations, etc.

codeforcescompetitive-programming
CF 105692L - ChaseDreamer

The problem statement is missing from your prompt, so there isn’t enough information to write a correct editorial.

codeforcescompetitive-programming
CF 105692K - The Tree Problem

Absolutely. Please provide the Codeforces problem (either the problem statement, problem ID such as "CF 1902C", or a link), and I'll write a competitive-programming editorial in the style commonly seen after contests. The editorial can include: 1.

codeforcescompetitive-programming
CF 105692J - Pseudo Merge Sort

I can’t reliably write a correct Codeforces editorial for 105692J - Pseudo Merge Sort without the actual problem statement.

codeforcescompetitive-programming
CF 105692I - Expected Value

I can’t produce a correct editorial yet because the actual problem content is missing. Right now I only have the title “Codeforces 105692I - Expected Value”, but no definition of the random process, input format, or what exactly is being computed.

codeforcescompetitive-programming
CF 105692H - The Easiest Problem

I can absolutely write a full editorial of that form, but I first need the complete problem statement or at least the official samples.

codeforcescompetitive-programming
CF 105692C - Dominoes Covering

We are given a binary target string representing a line of cells, initially all white. The only allowed operation acts on two adjacent cells: when we pick an index $i$, we forcibly set cell $i$ to white and cell $i+1$ to black, regardless of their previous state.

codeforcescompetitive-programming
CF 105692A - Chtholly Tree

I can’t write a correct editorial for this yet because the actual problem statement for “Codeforces 105692A - Chtholly Tree” isn’t included, and I don’t have reliable access to its content.

codeforcescompetitive-programming
CF 105692F - Big Baozi, Small Baozi

I can absolutely write a full editorial in the format you requested, but I don't have the actual problem statement for Codeforces Gym 105692F - Big Baozi, Small Baozi.

codeforcescompetitive-programming
CF 105691C - Gears

I can't accurately write this editorial because the prompt identifies the problem as "Codeforces 105691C - Gears", but the actual problem statement is missing.

codeforcescompetitive-programming
CF 105691B - RecoveriT

I cannot responsibly write a correct Codeforces-style editorial for 105691B - RecoveriT yet because the actual problem statement is not available in the context you provided, and it is not accessible from the retrieved sources.

codeforcescompetitive-programming
CF 105335A - Auntie's Magical Cake

Sure - I can do that, but I’ll need the actual problem first. Please paste the Codeforces problem statement (or at least the link / name), and if you want a specific style, tell me: - short editorial vs.

codeforcescompetitive-programming
CF 105335H - Heavenly Sequence

We are given a growing array where after each step we only consider a prefix of the array. For each prefix, we need to determine a parameter $K$ under a constraint involving a second parameter $X$, which is chosen from a given interval.

codeforcescompetitive-programming
CF 105335E - Executive's Holidays

I can’t write a correct editorial for this problem yet because the actual statement is missing. Right now I only see “E” with empty input and output sections, which doesn’t give any information about what is being asked, what the operations are, or what constraints drive…

codeforcescompetitive-programming
CF 105691A - A boring party!

The task describes a small game played with numbers where each number contributes a value equal to itself, but choosing a number has a side effect: it “removes” its immediate neighbors in value.

codeforcescompetitive-programming
CF 105692G - Find the Second Maximum

The task is about extracting order information from a collection of numbers: given a sequence, we want to identify not only the largest value, but also the value that is immediately below it in the ordering when duplicates are ignored.

codeforcescompetitive-programming
CF 105692E - OIer's Dream(Chaser)

We build the solution by scanning possible gcd values from large to small and maintaining which array elements are available for each gcd class. 1. Preprocess the frequency of each value in the array.

codeforcescompetitive-programming
CF 105692D - Coprime

We are asked to fill an $n times n$ grid with the integers from $1$ to $n^2$, each used exactly once, so the grid is a permutation of that range arranged in matrix form.

codeforcescompetitive-programming
CF 105692B - GoGo

The task is to simulate a very small programming language and determine what happens when a given script is executed. The script looks like a single function body starting from func main() and ending at its closing brace.

codeforcescompetitive-programming
CF 1056964 - Разрез

Sure - I can do that. Please paste the full Codeforces problem statement (or at least the link / name + constraints).

codeforcescompetitive-programming
CF 1056961 - Близкие друзья

I’m missing the actual problem statement here, and the identifier also looks a bit off for a Codeforces problem ID (it may be a contest task reference like “1056 E1” or similar, but as written I can’t reliably reconstruct it).

codeforcescompetitive-programming
CF 1056962 - Минимум

I can’t reliably write a correct Codeforces editorial for 1056962 - “Минимум” without the actual problem statement. Right now the input/output sections are empty, and there are multiple different problems that could plausibly share that name.

codeforcescompetitive-programming
CF 1056963 - Феникс

I can do that, but I’ll need the problem first. Please paste the Codeforces problem statement (or link + key details like constraints).

codeforcescompetitive-programming
CF 1056974 - Боб и Босс Файтинг

The problem statement section is empty, so there’s no way to reconstruct what “Боб и Босс Файтинг” is actually asking. Without the actual rules, inputs, and required output, any editorial would be guesswork and would very likely be wrong.

codeforcescompetitive-programming
CF 1056971 - Настоящие друзья

Each natural number greater than 1 is assigned a “friend”, defined as its largest proper divisor, meaning the biggest number strictly smaller than it that still divides it exactly. For example, 6 has proper divisors 1, 2, 3, and its friend is 3.

codeforcescompetitive-programming
CF 1056972 - Простой феникс

I can write the full editorial in exactly that style, but I’m missing the actual problem statement for “Codeforces 1056972 - Простой феникс”.

codeforcescompetitive-programming
CF 1056973 - Дело о делимости

I can’t reliably write a correct editorial for this yet because the actual problem statement is missing from your message (the sections for input/output are empty).

codeforcescompetitive-programming
CF 105705D - Simple Tree

The input describes a tree, meaning a connected undirected graph with no cycles, where each node carries an integer label.

codeforcescompetitive-programming
CF 105705B - Segment Trees ?

We maintain a sequence of integers. Over time, we are allowed to perform two actions. One action directly changes a single position in the array to a new value.

codeforcescompetitive-programming