brain

tamnd's digital brain — notes, problems, research

41230 notes

CF 103098A - Adjacent Rooks

We are given multiple test cases. Each test case describes an $n times n$ chessboard and asks us to place exactly $n$ rooks on the board so that no two rooks share a row or a column.

codeforcescompetitive-programming
CF 103119I - Nim Cheater

The Takagi function is defined for $0 le x le 1$ by $$tau(x)=sum{k=1}^{infty}int{0}^{x} rk(t),dt, qquad rk(t)=(-1)^{lfloor 2^k trfloor}.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 78

Let $\kappa_t$ denote the function defined in Section 7.

taocpmathematicsalgorithmsvolume-4math-medium
CF 103119B - Boring Problem

We are given a random string construction process. You start with an initial string, and repeatedly append one character at a time. Each character is chosen independently from a fixed alphabet of size k, with known probabilities.

codeforcescompetitive-programming
CF 103119D - Artifacts

We are given five artifact items, one for each equipment slot. Each artifact contributes exactly five stat lines, and across all artifacts we only care about four statistics: flat ATK, ATK percentage, Crit Rate, and Crit Damage.

codeforcescompetitive-programming
CF 103113L - Конструирование Резисторов

Let $q$ be a primitive $m$th root of unity, so $q^m=1$ and $q^jneq 1$ for $1le j<m$. Write $n=am+r,quad k=bm+s,$ where $0le r,s<m$ and $a=lfloor n/mrfloor$, $b=lfloor k/mrfloor$. The Gaussian binomial coefficient is $binom{n}{k}q=frac{[n]q!}{[k]q!,[n-k]q!},qquad [t]q!

codeforcescompetitive-programming
CF 103113K - Подсчет Графов

I don’t have the actual problem statement for Codeforces 103113K - “Подсчет Графов”, so I can’t reconstruct the intended solution or write a correct editorial yet.

codeforcescompetitive-programming
CF 103113J - Строковый Ад

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title “Строковый Ад”, but no description of what the input represents, what operations are allowed, or what needs to be computed.

codeforcescompetitive-programming
CF 103113A - Уравнение с НОК

Let $q$ be a primitive $m$th root of unity, so $q^m=1$ and $q^jneq 1$ for $1le j<m$. Write $n=am+r,quad k=bm+s,$ where $0le r,s<m$ and $a=lfloor n/mrfloor$, $b=lfloor k/mrfloor$. The Gaussian binomial coefficient is $binom{n}{k}q=frac{[n]q!}{[k]q!,[n-k]q!},qquad [t]q!

codeforcescompetitive-programming
CF 103113I - Улучшение Навыков

The problem statement is missing from your message (the sections for “Problem”, “Input”, and “Output” are empty), so I don’t have enough information to write a correct editorial.

codeforcescompetitive-programming
CF 103113H - Строим Параллелограммы~--- 2

The problem statement is missing from what you provided. Right now I only see the title “Constructing Parallelograms - 2”, but no description, input format, or output requirements.

codeforcescompetitive-programming
CF 103113G - За Орду!

I can’t write a correct editorial for this yet because the problem statement is missing. “Codeforces 103113G - За Орду!

codeforcescompetitive-programming
CF 103113F - Прочтите Условие Задачи

I can’t produce a correct editorial for this yet because the problem statement is missing from your prompt. Right now, only the title and metadata are provided, but there is no description of the task, no input format, no output format, and no constraints.

codeforcescompetitive-programming
CF 103113E - Битовая Магия

The problem statement for Codeforces 103113E - “Битовая Магия” is not included in your prompt, so there is no reliable way to reconstruct the intended task or derive a correct editorial.

codeforcescompetitive-programming
CF 103113D - Стековая Машина Возвращается

We are missing the actual problem statement for Codeforces 103113D - “Стековая Машина Возвращается”.

codeforcescompetitive-programming
CF 103113B - Странный Порядок

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title “Странный Порядок”, but there’s no description of the input, output, or the rules that define the task.

codeforcescompetitive-programming
CF 103113C - Теория Игр

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 103113C - Теория Игр” only gives the title, but there are no rules of the game, input/output format, or constraints.

codeforcescompetitive-programming
CF 103102M - Mistake

I can’t write a correct editorial for Codeforces 103102M - Mistake because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 103102L - Neo-Robin Hood

The problem statement is missing from your prompt, so I don’t have the actual task definition, constraints, or input/output format needed to write a correct Codeforces-style editorial.

codeforcescompetitive-programming
CF 103102A - Archeologists

Let $q$ be a primitive $m$th root of unity, so $q^m=1$ and $q^jneq 1$ for $1le j<m$. Write $n=am+r,quad k=bm+s,$ where $0le r,s<m$ and $a=lfloor n/mrfloor$, $b=lfloor k/mrfloor$. The Gaussian binomial coefficient is $binom{n}{k}q=frac{[n]q!}{[k]q!,[n-k]q!},qquad [t]q!

codeforcescompetitive-programming
CF 103102K - Codenames

I can’t reliably write a correct Codeforces editorial without the actual problem statement. “103102K - Codenames” isn’t something I can reconstruct from the title alone, and guessing would very likely produce a misleading solution, especially since the required structure…

codeforcescompetitive-programming
CF 103102J - One Piece

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only know the title “103102J - One Piece”, but there is no description of what the input represents, what operations are allowed, or what needs to be computed.

codeforcescompetitive-programming
CF 103102I - Modulo Permutations

I can’t reliably write a correct Codeforces editorial for 103102I - Modulo Permutations without the actual problem statement.

codeforcescompetitive-programming
CF 103102F - Fence Job

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now there’s no description of what “Fence Job” asks, what the input/output represent, or what constraints apply.

codeforcescompetitive-programming
CF 103102E - Divisible by 3

We are given an array of integers, and we need to count how many contiguous subarrays have a certain “pairwise product sum” divisible by 3. More precisely, take any subarray. Its value is defined as the sum of all products of pairs of elements inside it.

codeforcescompetitive-programming
CF 103102B - Reverse Game

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only know the contest ID and title (“Reverse Game”), but not the rules, input format, or what needs to be computed.

codeforcescompetitive-programming
CF 103102D - Disk Sort

I can write the full Codeforces-style editorial, but I don’t have the actual statement of CF 103102D - Disk Sort available from your prompt.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 77

For a positive integer $N$, write its $t$-binomial representation \kappa_t N = \binom{n_t}{t} + \binom{n_{t-1}}{t-1} + \cdots + \binom{n_1}{1}, where $n_t > n_{t-1} > \cdots > n_1 \ge 0$ is the unique...

taocpmathematicsalgorithmsvolume-4math-hard
TAOCP 7.2.1.3 Exercise 76

The function $\kappa_t N$ arises from the combinatorial number system in which an integer $N$ is written uniquely in the form N = \binom{n_t}{t} + \binom{n_{t-1}}{t-1} + \cdots + \binom{n_v}{v}, with...

taocpmathematicsalgorithmsvolume-4math-medium
CF 103102H - AND = OR

We are given an array of integers, and we are interested in contiguous segments of this array where a bitwise condition holds: the bitwise AND of all elements in the segment is exactly equal to the bitwise OR of all elements in the same segment.

codeforcescompetitive-programming
CF 103102G - Simple Hull

The problem describes a collection of points in a 2D plane and asks us to construct the “simple hull” of these points.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 75

The representation (57) expresses a positive integer $N$ in degree-$t$ combinatorial form by selecting an index $v$ such that \binom{n}{t} > N \ge \binom{n}{t} - \binom{v}{t}, and then writing $N$ as...

taocpmathematicsalgorithmsvolume-4math-medium
CF 103102C - 3-colorings

We are asked to construct a very small graph on at most 19 vertices with a deliberately chosen structure, then later, without knowing a parameter $k$, we are allowed to add up to 17 extra edges depending on $k$, so that the final number of proper 3-colorings of the graph…

codeforcescompetitive-programming
CF 103104K - Chtholly and World-End Battle

We are given a static array of integers and a sequence of queries. Each query specifies a subarray range and an initial value. To process a query, we start from the given value v and scan the array elements from left to right within the range [l, r].

codeforcescompetitive-programming
CF 103104I - Sequence

Connection interrupted. Waiting for the complete answer

codeforcescompetitive-programming
CF 103104H - Information Transmission

We are given a directed communication network of stations. Each station can forward a message to some other stations along directed links. A message starts at station 1 and is repeatedly relayed until it possibly reaches other stations.

codeforcescompetitive-programming
CF 103104J - Similar Triangles

We are given a triangle with integer coordinates in the plane. The task is not to compute any property of this triangle directly, but instead to construct a different triangle, also with integer coordinates, that is similar to the given one while having the smallest possible…

codeforcescompetitive-programming
CF 103104G - Crossword Puzzle

We are given a crossword grid drawn as a large ASCII picture. Each logical cell of the crossword is a 5×5 block in the input, where borders are shared between neighboring cells.

codeforcescompetitive-programming
CF 103104A - CRC Test

Fix an integer $t ge 1$. Let $N ge 0$ be given. Define $kappat N$ in the discrete sense (as in earlier parts of Section 7.2.1.3) as the unique integer $m ge t-1$ such that $$binom{m}{t} le N < binom{m+1}{t},$$ and set $$kappat N = binom{m}{t-1}.

codeforcescompetitive-programming
CF 103104F - Battery

We are given a collection of batteries and a collection of shooting locations. Each battery has a fixed amount of energy, and each location requires a fixed amount of energy to complete one recording session.

codeforcescompetitive-programming
CF 103104E - Revue

We are given a sequence of interactions between numbered participants, each participant starting with some unknown but distinct “radiance” value.

codeforcescompetitive-programming
CF 103104D - Fragmentation merging

We are given a permutation of length $n$, and we interpret any pair of indices $(l, r)$ as a “fragmentation” that corresponds to the set of values in the segment $al, a{l+1}, dots, ar$ if $l le r$. If $l r$, that fragmentation represents an empty set.

codeforcescompetitive-programming
CF 103104C - Data structure

We are given two independent structures that interact through a color-mapping rule. On one side, we have a Huffman tree built from the first $K$ Fibonacci weights.

codeforcescompetitive-programming
CF 103104B - Mr.X and Reviewing Location

We are given a circular hall centered at the origin with radius $R$, and $n$ existing people inside it. Each person occupies a point in the plane, and we are guaranteed that every pair of existing people is at least 2 units apart.

codeforcescompetitive-programming
CF 103107L - Labi-Ribi

Fix an integer $t ge 1$. Let $N ge 0$ be given. Define $kappat N$ in the discrete sense (as in earlier parts of Section 7.2.1.3) as the unique integer $m ge t-1$ such that $$binom{m}{t} le N < binom{m+1}{t},$$ and set $$kappat N = binom{m}{t-1}.

codeforcescompetitive-programming
CF 103107H - Hack DSU!

I can write the full editorial, but I’m missing the actual problem statement for Codeforces 103107H - Hack DSU!. Right now I don’t know: what operations DSU supports in this problem, what “hack” means in context, or what the input/output is supposed to represent.

codeforcescompetitive-programming
CF 103107K - Keep Eating

For real $x ge t-1$, define the generalized binomial coefficients $$binom{x}{t} = frac{x(x-1)cdots(x-t+1)}{t!}, qquad binom{x}{t-1} = frac{x(x-1)cdots(x-t+2)}{(t-1)!}.

codeforcescompetitive-programming
CF 103107J - JOJO's Factory

I’m missing the actual problem statement for Codeforces 103107J - JOJO’s Factory, so I can’t reconstruct the model, constraints, or intended solution safely without guessing.

codeforcescompetitive-programming
CF 103107A - And RMQ

For real $x ge t-1$, define the generalized binomial coefficients $$binom{x}{t} = frac{x(x-1)cdots(x-t+1)}{t!}, qquad binom{x}{t-1} = frac{x(x-1)cdots(x-t+2)}{(t-1)!}.

codeforcescompetitive-programming
CF 103107I - ICU4C

The problem statement for Codeforces 103107I - ICU4C is missing from your prompt, so there’s no way to correctly reconstruct the task or produce a valid editorial.

codeforcescompetitive-programming
CF 103107G - Go? No

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 103107G - Go?

codeforcescompetitive-programming
CF 103107E - Elastic Search

We are given a collection of strings, all composed of lowercase letters. The task is not about processing them independently, but about understanding how they relate through containment structure between strings.

codeforcescompetitive-programming
CF 103107F - Function

I can’t reliably write a correct editorial for this because the actual problem statement for Codeforces 103107F - Function is missing from your prompt.

codeforcescompetitive-programming
CF 103107D - Doin' Time

The problem statement for “Codeforces 103107D - Doin' Time” is not included in your message, so I can’t reliably derive the solution or write a correct editorial.

codeforcescompetitive-programming
CF 103107C - Cookie

We are given two simple polygons, each described by its vertices in counterclockwise order. You can think of them as two “broken cookie pieces” lying in the plane after a convex cookie has been shattered.

codeforcescompetitive-programming
CF 103107B - Bo Bing

I can’t write a correct editorial for “Codeforces 103107B - Bo Bing” yet because the actual problem statement is not available from the information you provided, and the title alone is not enough to reliably reconstruct the task.

codeforcescompetitive-programming
CF 103109G - Scribble Roads

For real $x ge t-1$, define the generalized binomial coefficients $$binom{x}{t} = frac{x(x-1)cdots(x-t+1)}{t!}, qquad binom{x}{t-1} = frac{x(x-1)cdots(x-t+2)}{(t-1)!}.

codeforcescompetitive-programming
CF 103109L - Pillar Path

I can write the full editorial in the exact format you requested, but I’m missing the actual problem statement.

codeforcescompetitive-programming
CF 103109K - Kirby's Buffet

I don’t have the actual statement of Codeforces 103109K - Kirby's Buffet, so I can’t safely reconstruct the logic or write a correct editorial without guessing.

codeforcescompetitive-programming
CF 103109J - Luigi's Mansion

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

codeforcescompetitive-programming
CF 103109I - Immortality Potion

I can’t write a correct Codeforces editorial for “103109I - Immortality Potion” because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 103109H - Future Gadget Lab

The problem statement for Codeforces 103109H - Future Gadget Lab is missing from your prompt, so there is no way to reconstruct the intended task, constraints, or solution correctly.

codeforcescompetitive-programming
CF 103109E - Knockout Tournament

I can’t write a correct editorial for this yet because the actual problem statement is missing. “Codeforces 103109E - Knockout Tournament” isn’t enough on its own to reconstruct the rules, and anything I write without the full description would be guesswork (which would…

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 74

Corollary C establishes that an $(s,t)$-combination can be represented equivalently as a binary string $a_{n-1}\dots a_1a_0$ with $t$ ones, as a decreasing sequence $c_t>\cdots>c_1$, as the complement...

taocpmathematicsalgorithmsvolume-4math-medium
CF 103109A - Pokémon Permutation

Let $kappat$ be the function defined in the section, with inverse $mut$ in the sense that $$M ge mut N quad Longleftrightarrow quad kappat(M) ge N,$$ for $t ge 2$.

codeforcescompetitive-programming
CF 103109F - Squid Art

The problem statement is missing, so I can’t reliably reconstruct what Codeforces 103109F “Squid Art” is asking or derive a correct solution.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 73

Let $U$ denote the set underlying the multicombinations (92).

taocpmathematicsalgorithmsvolume-4math-medium
CF 103109D - Cytus Craze

The problem statement section is empty, so there is no way to reconstruct what “Cytus Craze” is asking us to compute. Without knowing the input format, the rules, or what constitutes a valid answer, any editorial would be pure invention rather than explanation.

codeforcescompetitive-programming
CF 103109C - Goomba Grouping

I cannot reliably reconstruct Codeforces 103109C - Goomba Grouping from the available context or standard archives, and the statement is not present in the prompt.

codeforcescompetitive-programming
CF 103109B - Azran Tablets

The problem statement section is empty, so I don’t actually have the definition of what “Azran Tablets” is asking us to compute. Without that, I can’t write a correct editorial, because everything from the solution strategy to the edge cases depends on the exact rules.

codeforcescompetitive-programming
CF 103110L - Squid Art

The problem statement is missing from your prompt, so I don’t actually know what “103110L - Squid Art” asks. Right now I can’t reconstruct: - what the input represents, - what transformation or computation is required, - or what the output should be.

codeforcescompetitive-programming
CF 103110E - Pokémon Permutation

Let $kappat$ be the function defined in the section, with inverse $mut$ in the sense that $$M ge mut N quad Longleftrightarrow quad kappat(M) ge N,$$ for $t ge 2$.

codeforcescompetitive-programming
CF 103110K - Rabbit Subtraction

The problem statement section is empty, so there’s no way to reconstruct what “Rabbit Subtraction” actually asks.

codeforcescompetitive-programming
CF 103110J - Goomba Grouping

The problem statement is missing from your prompt, so I don’t actually have the definition of what “Goomba Grouping” is, what the input describes, or what needs to be computed.

codeforcescompetitive-programming
CF 103110I - Grid Shuffling

The problem statement for “103110I - Grid Shuffling” is missing from your prompt, so I don’t have the actual rules of the task (what “shuffling” means, what operations are allowed, or what needs to be computed).

codeforcescompetitive-programming
CF 103110H - Street Layout

I can’t write a correct editorial for this yet because the actual problem content for Codeforces 103110H - Street Layout isn’t included in your prompt.

codeforcescompetitive-programming
CF 103110F - Island Isolation

I don’t have the actual problem statement for Codeforces 103110F - Island Isolation, so I can’t safely write a correct editorial yet.

codeforcescompetitive-programming
CF 103110G - Map Matching

I don’t have the actual statement of Codeforces 103110G - Map Matching, and without it I can’t reliably reconstruct the problem or write a correct editorial.

codeforcescompetitive-programming
CF 103110D - Apple Orchard

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 103110D - Apple Orchard is missing from your prompt.

codeforcescompetitive-programming
CF 103110C - Reverse Race

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “103110C - Reverse Race”, but no description of what the race rules are, what the input represents, or what needs to be computed.

codeforcescompetitive-programming
CF 103110A - Mountain Climbing

Let $n = s + t$. A Chase sequence $C{st}$ is a Gray-code ordering of all $(s,t)$-combinations, in which successive combinations differ by a single unit transfer of a $1$ across a contiguous block of $0$s in the binary representation, equivalently by updating the list…

codeforcescompetitive-programming
CF 103110B - Digit Sum

I’m missing the actual problem statement for “Codeforces 103110B - Digit Sum”, so I can’t reconstruct the intended task or derive a correct solution.

codeforcescompetitive-programming
CF 103112B - Клавиатура

Let $n = s + t$. A Chase sequence $C{st}$ is a Gray-code ordering of all $(s,t)$-combinations, in which successive combinations differ by a single unit transfer of a $1$ across a contiguous block of $0$s in the binary representation, equivalently by updating the list…

codeforcescompetitive-programming
CF 103112G - Квест

The editorial request is missing the only thing that actually determines the solution: the problem statement. “Codeforces 103112G - Квест” is not enough to reconstruct the task reliably, and guessing would almost certainly produce a wrong or irrelevant editorial.

codeforcescompetitive-programming
CF 103112F - Солдатская смекалка

I can write the full Codeforces-style editorial, but the problem statement for 103112F - “Солдатская смекалка” is missing from your message.

codeforcescompetitive-programming
CF 103112E - Фокусы

I don’t have the actual statement of Codeforces 103112E - Фокусы in your prompt, and without it I can’t reliably reconstruct the problem or produce a correct editorial.

codeforcescompetitive-programming
CF 103112D - Монеты для друзей

I can’t write a correct editorial yet because the actual problem statement for “103112D - Монеты для друзей” is missing from your prompt.

codeforcescompetitive-programming
CF 103112A - Номер сундука

I can’t write a correct editorial for this yet because the actual problem statement (what the “chest number” means, what the input describes, and what is required in the output) is missing.

codeforcescompetitive-programming
CF 103112C - Надпись

I can’t write a correct editorial for this yet because the actual problem statement for Codeforces 103112C - “Надпись” is missing from your prompt. Right now, I don’t know what the input represents, what transformations are allowed, or what needs to be computed.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 72

Theorem W is proved in Section 7.

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.2.1.3 Exercise 71

Let $G$ be a simple graph with $m=10^6$ edges, and let $K_t(G)$ denote the number of $t$-cliques in $G$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 103114H - Hsueh- and Meeting

Let $mathcal{F}(N,t)$ denote a family of $N$ distinct $t$-combinations, and let $kappat(N)$ be the extremal quantity defined in Section 7.2.1.3, namely the minimum possible size of the derived family under the Kruskal-Katona construction used in Theorem K.

codeforcescompetitive-programming
CF 103114J - Jahaxiki's journey III - Tryna lost

We are given a grid-like planar map where movement happens between small square cells. Each cell is potentially connected to its neighboring cells through openings, while barriers are represented implicitly by wall characters in a textual layout.

codeforcescompetitive-programming
CF 103114I - Iahaxiki's journey II - enjoying

We are given a weighted tree with $n$ vertices. Each edge connects two vertices and has a positive length. The task is to choose a simple path in this tree such that the path contains exactly $k$ vertices, and among all such paths we want the one with the maximum possible…

codeforcescompetitive-programming
CF 103114G - Guess Permutation

We are given a hidden permutation of the numbers from 1 to n, stored across positions 1 to n. Our task is to recover the entire permutation, meaning we must determine the exact value at every position. The only way to obtain information is through queries.

codeforcescompetitive-programming
CF 103114F - Fstee1XD and Minioins

The process described in this problem is a deterministic population growth system where each individual has an age-dependent reproduction rule. We start with a single minion born on day one.

codeforcescompetitive-programming
CF 103114B - Bsueh- and Gold Medals

Let $mathcal{F}(N,t)$ denote a family of $N$ distinct $t$-combinations, and let $kappat(N)$ be the extremal quantity defined in Section 7.2.1.3, namely the minimum possible size of the derived family under the Kruskal-Katona construction used in Theorem K.

codeforcescompetitive-programming
CF 103114E - Ewo Slices of Bread with Cheese

We are given a collection of cheese pieces, each with an initial freshness value. Time advances in discrete days. Every day, all remaining pieces simultaneously lose one unit of freshness.

codeforcescompetitive-programming
CF 103114D - Dllllan and his friends

We are given a set of points on the plane, each representing a friend’s house. We need to choose a single point, interpreted as the location of a new home, and also compute a travel cost associated with visiting all friends from that home.

codeforcescompetitive-programming
CF 103114C - Chtholly and Floating Islands

We are given a line of numbered islands starting from island 1 up to island n. From any island j, Chtholly can jump forward by adding one value from a set of available “step sizes”, meaning she moves from j to j + x where x is chosen from her current ability list.

codeforcescompetitive-programming