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tamnd's digital brain — notes, problems, research

41641 notes

CF 104027J - runaway problem

I can’t write a correct editorial from that input because the actual problem content is missing. Right now I only see: There is no statement, no description of what “runaway” refers to, and no constraints.

codeforcescompetitive-programming
CF 104027H - 还是分糖果

We are given two sequences, call them A and B. Each query gives us two prefixes: A[1..x] and B[1..y]. The task is to decide whether these two prefixes “match in terms of distinct elements” in a symmetric way: every value that appears in the prefix of A must already appear in…

codeforcescompetitive-programming
CF 104027I - jump

I can’t write a correct editorial for “Codeforces 104027I - jump” without the actual problem statement. That code alone isn’t enough to reliably reconstruct the task, and guessing would risk producing a completely wrong solution and explanation.

codeforcescompetitive-programming
CF 104027G - 三角力量

We are given an undirected graph, but unlike the standard simple version, between any two vertices there may be multiple edges. Each pair of vertices can be connected by several parallel edges, and those parallel edges all count as distinct choices when forming structures.

codeforcescompetitive-programming
CF 104027C - 异或

Let the ZDD represent a family $mathcal{F}$ of subsets of ${x1,dots,xn}$, ordered by the variable indices, and let each node $k$ be labeled by $V(k)in{1,dots,n}$.

codeforcescompetitive-programming
CF 104027F - 落石

The problem models a collection of stone blocks falling vertically onto a one dimensional ground made of columns. Each column starts empty at height zero, and as stones are dropped, they stack upward depending on where they land.

codeforcescompetitive-programming
CF 104027E - 技能加点

The problem describes a character-building style optimization where you distribute a limited number of skill points between two attributes, denoted as E and R.

codeforcescompetitive-programming
CF 104027D - 饱了没红包

We are given a sequence of orders, each with a price, and a collection of discount coupons. Each coupon has a threshold value and a discount value. A coupon can only be applied to an order if the order price is at least as large as the coupon’s threshold.

codeforcescompetitive-programming
CF 104027A - lzd的人生经验

The task is essentially a reading-comprehension style simulation compressed into arithmetic. We are given a description of some process that consumes time, along with a limit in seconds, denoted by $m$.

codeforcescompetitive-programming
CF 104027B - Candies

We are given a collection of candy packs. Each pack contains either 2 candies or 3 candies. The task is to determine whether it is possible to distribute all candies among three people so that each person receives exactly the same total number of candies.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 64

Let $B(f)$ denote the number of beads of a Boolean function $f$, equivalently the number of nodes in its reduced ordered BDD.

taocpmathematicsalgorithmsvolume-4math-medium
CF 104030K - Keyboard Queries

We are given a hidden string indexed from 1 to n. We never see the characters directly. Instead, we receive two kinds of information about it. The first type of query tells us that a certain substring is guaranteed to read the same forward and backward.

codeforcescompetitive-programming
CF 104030J - Junk Journey

The problem gives us an infinite grid with a small number of special cells: a starting position for a robot, a target cell called the depot, and up to 50 scooters placed at distinct grid coordinates. The robot moves one step at a time in the four cardinal directions.

codeforcescompetitive-programming
CF 104030G - Graduation Guarantee

Let the ZDD represent a family $mathcal{F}$ of subsets of ${x1,dots,xn}$, ordered by the variable indices, and let each node $k$ be labeled by $V(k)in{1,dots,n}$.

codeforcescompetitive-programming
CF 104030H - Highest Hill

We are given a long sequence of terrain heights sampled at evenly spaced positions. From this sequence, we want to identify a special kind of “peak” defined by choosing three indices i, j, k with i < j < k such that the height first does not decrease up to j and then does…

codeforcescompetitive-programming
CF 104030I - Icy Itinerary

We are given a town modeled as an undirected graph on n houses. Some pairs of houses are connected by roads, and every other pair is considered connected only by an implicit “non-road” relation, meaning Thomas must travel between them using skis.

codeforcescompetitive-programming
CF 104030E - Enigmatic Enumeration

We are given an undirected simple graph. The task is not to find just one cycle, but to determine how many cycles achieve the minimum possible length among all cycles in the graph.

codeforcescompetitive-programming
CF 104030F - Foreign Football

We are given a hidden set of $n$ strings, one per football team, and every pair of distinct teams produces a recorded match string that is simply the concatenation of the two team names in order.

codeforcescompetitive-programming
CF 104030B - Berry Battle

Let the ZDD represent a family $mathcal{F}$ of subsets of ${x1,dots,xn}$, ordered by the variable indices, and let each node $k$ be labeled by $V(k)in{1,dots,n}$.

codeforcescompetitive-programming
CF 104030D - Disc District

We are given a circle centered at the origin in the plane, with radius $r$. Every point whose distance from the origin is strictly greater than $r$ is considered outside the circle.

codeforcescompetitive-programming
CF 104030A - Ace Arbiter

We are given a chronological log of score snapshots from a ping pong game between two players. The game ends as soon as one player reaches 11 points, and no further points should exist beyond that moment.

codeforcescompetitive-programming
CF 104030C - Coffee Cup Combo

We are given a sequence of n lectures arranged in order. Each lecture either has a coffee machine or does not. The student starts before the first lecture with no coffee cups, and during each lecture she must consume exactly one cup in order to stay awake.

codeforcescompetitive-programming
CF 104031D - Экскаватор

We are given a chronological stream of events describing work requests arriving from different sites, and a single excavator that moves between sites and spends a fixed number of days working at each site it visits.

codeforcescompetitive-programming
CF 104031C - Роллер

Let $A={i1,i2,ldots,iell}$ and let $F = e{i1}cupcdotscup e{iell}$. The ZDD for $F$ consists of a single decision chain ordered by indices, because each $e{it}$ contributes a node that tests membership of $it$ and reduces to $perp$ or $top$ as in the conventions of Exercise 7.1.4.

codeforcescompetitive-programming
CF 104031E - Котики

We are simulating a process where a person interacts repeatedly with cats of different breeds, and the only thing that matters is the order in which each breed was last seen or last interacted with. Each operation can be interpreted as a request involving a cat breed.

codeforcescompetitive-programming
CF 104031B - Примеры

Two students solve a sequence of problems one after another. Kesha spends a fixed amount of time per problem, call it $tk$, and Melentiy spends $tm$. They both start at the same moment and work continuously until a decision moment called “going for a walk”.

codeforcescompetitive-programming
CF 104031A - Водонагреватель

The problem describes a device that consumes energy while operating for a fixed duration, but the cost per minute depends on which time-of-day tariff is active. There are two tariffs, each defined by a price per minute and a time interval during the day when it applies.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 63

Let $M_m$ denote the majority function on $m$ Boolean inputs, defined in Section 7.

taocpmathematicsalgorithmsvolume-4math-hard
CF 1040332 - Центральные квадраты

Let $A={i1,i2,ldots,iell}$ and let $F = e{i1}cupcdotscup e{iell}$. The ZDD for $F$ consists of a single decision chain ordered by indices, because each $e{it}$ contributes a node that tests membership of $it$ and reduces to $perp$ or $top$ as in the conventions of Exercise 7.1.4.

codeforcescompetitive-programming
CF 1040334 - Спираль

I’m missing the actual problem statement for Codeforces 1040334 - “Спираль”, and without it I can’t produce a correct editorial.

codeforcescompetitive-programming
CF 1040335 - Надпись на табло

The problem statement for Codeforces 1040335 - “Надпись на табло” is not included in your message, and I don’t have enough information to reconstruct the task reliably.

codeforcescompetitive-programming
CF 1040331 - Лягушка и кузнечик

The state of the system can be viewed through two positions: the frog position $f$ starting from 1 and increasing, and the grasshopper position $g$ starting from $N$ and decreasing. At every second, $f$ increases by either 2 or 3, while $g$ decreases by either 1 or 2.

codeforcescompetitive-programming
CF 1040333 - Заказ в магазине

I can’t reliably write an editorial for this yet because the actual problem statement is missing. “Codeforces 1040333 - Заказ в магазине” only gives a title, but the required solution, constraints, and even the meaning of input/output are not included in your…

codeforcescompetitive-programming
CF 1040344 - Лука и массив

We start with an array where each value behaves like a token sitting on a number line. The allowed moves are either a small step left by one unit costing 1 energy, or a large jump to floor(x/2) costing k energy.

codeforcescompetitive-programming
CF 1040345 - Лука и локальная сеть динозавров

I’m missing the actual problem statement for “Codeforces 1040345 - Лука и локальная сеть динозавров”.

codeforcescompetitive-programming
CF 1040343 - Лука наблюдает за кузнечиками

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

codeforcescompetitive-programming
CF 1040341 - Лука в кинотеатре

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only have the title “Лука в кинотеатре” (Luka in the cinema), but no description of what Luka is supposed to compute, what the inputs are, or what…

codeforcescompetitive-programming
CF 1040342 - Лука покупает динозавров

The problem statement is missing from the prompt, so there is no way to reconstruct the required reasoning, constraints, or solution correctly.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 62

Algorithm D in Section 7.

taocpmathematicsalgorithmsvolume-4math-medium
CF 1040354 - Браслет

I can’t reliably produce a correct editorial yet because the actual problem statement for “1040354 - Браслет” is not visible/complete from the provided material, and the Codeforces reference in your prompt does not uniquely identify a single stable statement (there…

codeforcescompetitive-programming
CF 1040355 - Задача о числах

The problem statement for “Codeforces 1040355 - Задача о числах” isn’t included in your message, so I don’t have enough information to write a correct editorial.

codeforcescompetitive-programming
CF 1040353 - Длина числа

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only have the title “Длина числа” (“Length of a number”), but no input format, constraints, or task definition.

codeforcescompetitive-programming
CF 1040352 - Разноэтажный дом

The problem statement section is empty, so there isn’t enough information to reconstruct what Codeforces 1040352 - “Разноэтажный дом” is actually asking.

codeforcescompetitive-programming
CF 1040351 - Время в школе

I can’t reliably write a correct Codeforces-style editorial here because the actual problem statement for “1040351 - Время в школе” is missing from your prompt.

codeforcescompetitive-programming
CF 1040361 - Треугольник из палочек

Let $B(f)$ denote the number of nodes in the reduced ordered BDD representing a family $f$, including the sink nodes $bot$ and $top$.

codeforcescompetitive-programming
CF 1040364 - Платные музыкальные сервисы

I can’t reliably write a correct editorial yet because the actual Codeforces problem statement for “1040364 - Платные музыкальные сервисы” is not available in the provided content, and it is not a standard public problem I can uniquely identify…

codeforcescompetitive-programming
CF 1040365 - Линейный футбол

I can’t write a correct editorial yet because the actual problem statement for “Codeforces 1040365 - Линейный футбол” is not included in your prompt, and the identifier does not directly resolve to a standard Codeforces problem I can safely assume.

codeforcescompetitive-programming
CF 1040362 - Раскрашенный куб

I don’t have the actual statement of Codeforces 1040362 “Раскрашенный куб” in your message, so I can’t reliably reconstruct the solution or write a correct editorial without risking inventing details.

codeforcescompetitive-programming
CF 1040363 - Антон и арбузы

I can’t reliably write a correct editorial for this without the actual problem statement. “Codeforces 1040363 - Антон и арбузы” isn’t enough to reconstruct the task, and guessing would very likely produce a completely wrong solution and reasoning.

codeforcescompetitive-programming
CF 104037C - Expr

Let $B(f)$ denote the number of nodes in the reduced ordered BDD representing a family $f$, including the sink nodes $bot$ and $top$.

codeforcescompetitive-programming
CF 104037D - Point

I can write this editorial in exactly the style you want, but I’m missing the actual problem content. “Codeforces 104037D - Point” isn’t something I can reliably reconstruct from the title alone, and I don’t want to hallucinate constraints, operations, or intended…

codeforcescompetitive-programming
CF 104037A - Power

I don’t have the statement of Codeforces 104037A - Power available in context, and this ID doesn’t correspond to a standard Codeforces problem I can reliably reconstruct.

codeforcescompetitive-programming
CF 104037B - Decode

I can write the full editorial in exactly that format, but I’m missing the actual problem statement for Codeforces 104037B - Decode.

codeforcescompetitive-programming
CF 104048J - Knight In Shining Armor 1

Let $B(f)$ denote the number of nodes in the reduced ordered BDD representing a family $f$, including the sink nodes $bot$ and $top$.

codeforcescompetitive-programming
CF 104048K - Fullmetal Alchemist II

We are given up to ten short phrases, each being a string of lowercase letters. The task is to construct a single combined phrase that contains every given phrase as a substring.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 61

Let $f$ and $g$ be Boolean functions with respective BDDs.

taocpmathematicsalgorithmsvolume-4math-hard
CF 104048I - Meteoric Sword

I don’t have the actual statement for Codeforces 104048I - Meteoric Sword in your prompt, so I can’t write a correct editorial yet without guessing the problem structure.

codeforcescompetitive-programming
CF 104048H - Alluring Alloy

We are given a single string representing an initial alloy recipe. Each character is a type of metal. The only allowed operation is to take a character that originally existed in the input and duplicate it exactly once, placing the copy adjacent to the original occurrence.

codeforcescompetitive-programming
CF 104048A - Copper Corners

Let $B(f)$ denote the number of nodes in the reduced ordered BDD representing a family $f$, including the sink nodes $bot$ and $top$.

codeforcescompetitive-programming
CF 104048G - Foil Folding

The problem statement for “Codeforces 104048G - Foil Folding” is missing from your prompt, so I don’t have the actual rules of the task, input format, or what needs to be computed.

codeforcescompetitive-programming
CF 104048F - Neodymium Gravity

I can write the full editorial in exactly that style, but I’m missing the actual problem content for Codeforces 104048F - Neodymium Gravity.

codeforcescompetitive-programming
CF 104048E - Steel Customs

I can’t write a correct editorial yet because the actual problem content for “Codeforces 104048E - Steel Customs” is missing from your prompt.

codeforcescompetitive-programming
CF 104048D - Fullmetal Alchemist I

I don’t have the statement of Codeforces 104048D - Fullmetal Alchemist I available in this context, and I can’t reliably reconstruct it from the title alone without risking inventing details.

codeforcescompetitive-programming
CF 104048B - Foo Bar

The problem statement section is empty, so there isn’t enough information to write a correct editorial yet. For Codeforces problems, even small details like what “Foo Bar” actually does, how input is structured, and what transformations are required completely change the…

codeforcescompetitive-programming
CF 104048C - Capturing Bronze

I can’t reliably reconstruct the full statement of Codeforces 104048C - Capturing Bronze from public sources, and I don’t want to invent a problem and then build a fake editorial around it.

codeforcescompetitive-programming
CF 104049K - Fullmetal Alchemist II

We represent a family $f$ as a reduced ordered decision diagram over variables $x1,x2,dots,xn$, using the conventions of Section 7.1.4 and Exercise 203. A node $v$ has fields $$V(v),quad LO(v),quad HI(v),$$ and terminals $bot,top$.

codeforcescompetitive-programming
CF 104049M - Knight in Shining Armor 2

I can’t write a correct editorial for that problem yet because the statement content is missing. “Codeforces 104049M - Knight in Shining Armor 2” isn’t available in your prompt, and without the actual rules (what the knight does, what the input/output represent…

codeforcescompetitive-programming
CF 104049L - Loid Forger

I can’t reliably write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title “104049L - Loid Forger”, but none of the details about the input, output, or task.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 60

Let $f$ and $g$ be reduced ordered BDDs over variables $x_1,\dots,x_n$ with fixed ordering.

taocpmathematicsalgorithmsvolume-4math-medium
CF 104049J - Knight In Shining Armor 1

I can’t write a correct editorial yet because the problem statement for Codeforces 104049J - Knight In Shining Armor 1 is missing from your prompt.

codeforcescompetitive-programming
CF 104049C - Capturing Bronze

We represent a family $f$ as a reduced ordered decision diagram over variables $x1,x2,dots,xn$, using the conventions of Section 7.1.4 and Exercise 203. A node $v$ has fields $$V(v),quad LO(v),quad HI(v),$$ and terminals $bot,top$.

codeforcescompetitive-programming
CF 104049I - Meteoric Sword

I can’t produce a correct editorial yet because the actual problem statement for Codeforces 104049I - Meteoric Sword is missing from your prompt.

codeforcescompetitive-programming
CF 104049G - Foil Folding

We are given a rectangular sheet of foil represented as a grid of size $n times m$. Some cells contain imperfections marked as X, while others are clean. From this sheet, we want to extract a rectangular piece of metal that qualifies as an ingot.

codeforcescompetitive-programming
CF 104049H - Alluring Alloy

The problem statement for Codeforces 104049H - Alluring Alloy is missing from your prompt, so I don’t have enough information to reconstruct the task or derive the algorithm.

codeforcescompetitive-programming
CF 104049F - Neodymium Gravity

I can write the full editorial in that format, but I’m missing the actual problem statement for Codeforces 104049F - Neodymium Gravity. Right now I only have the contest/problem identifier, not what the task is asking (input format, operations, constraints, etc.).

codeforcescompetitive-programming
CF 104049D - Fullmetal Alchemist I

I can’t reliably write a correct editorial for Codeforces 104049D - Fullmetal Alchemist I without the actual problem statement.

codeforcescompetitive-programming
CF 104049E - Steel Customs

I don’t have the statement of Codeforces 104049E - Steel Customs available from the prompt, and I can’t reliably reconstruct the problem from the title alone without risking inventing details.

codeforcescompetitive-programming
CF 104052D - Lost in Translation

We are given a binary string and we need to transform it into a string over a three-letter alphabet, typically A, B, and C, in such a way that the original binary string can still be uniquely reconstructed even after an adversarial deletion process that removes all occurrences…

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 59

Let $H$ denote the reduced ordered BDD for $h(x_1,\ldots,x_n)$.

taocpmathematicsalgorithmsvolume-4math-hard
CF 104052E - Summer School

We are given a bipartite structure where one side consists of students and the other side consists of slots, referred to as parallels. Each student is connected to some subset of these slots, and a connection means that the student is eligible to be assigned to that slot.

codeforcescompetitive-programming
CF 104052C - Sliding Dominoes

The solution answers all parts, but part (b) is incorrect and breaks subsequent reasoning. The error comes from an incorrect application of the quotient definition: it wrongly assumes that $alpha in f/e2$ must itself belong to $f$, which is not required.

codeforcescompetitive-programming
CF 104052B - Lunchtime Fruits

We are given four non-negative integers describing how many items we have of four types, A, B, C, and D. From these items we want to assemble identical “sets”, and each set must be one of three fixed patterns: One pattern consumes two A items, one B item, and one C item.

codeforcescompetitive-programming
CF 104052A - Sheet Metal

The problem can be viewed as a sequence of levels, where each level contributes some number of elements, and also comes with an interval that describes where its influence applies.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 58

We begin by making the construction in (37) explicit in the only way the proof can depend on it.

taocpmathematicsalgorithmsvolume-4medium
CF 104053M - XOR Sum

We are given a sequence of length $k$, where each element $ai$ is a non-negative integer bounded by $m$. For any such sequence, its value is defined as the sum over all pairs where the second index does not exceed the first, of the bitwise XOR of the pair: $$sum{i=1}^{k}…

codeforcescompetitive-programming
CF 104053J - Math Exam

The solution answers all parts, but part (b) is incorrect and breaks subsequent reasoning. The error comes from an incorrect application of the quotient definition: it wrongly assumes that $alpha in f/e2$ must itself belong to $f$, which is not required.

codeforcescompetitive-programming
CF 104053L - Station of Fate

We are given a scenario where $n$ distinct people are to be arranged into $m$ labeled stations, and each station holds a queue. A queue here is not just a set, but an ordered list, so the internal ordering of people inside each station matters.

codeforcescompetitive-programming
CF 104053K - Middle Point Graph

Each vertex of a connected undirected graph is turned into a random point in 3D space. The coordinates of a vertex are independent uniform real numbers in the unit cube, so every vertex gets a completely independent random position.

codeforcescompetitive-programming
CF 104053I - Infection

We are given a tree with n nodes. One node is chosen as the initial infection source, and that choice is random but weighted: node i is selected with probability proportional to ai.

codeforcescompetitive-programming
CF 104053G - Game

Two players repeatedly build up numbers by multiplying chosen integers. Alice controls set $A$, Bob controls set $B$. Both start with values $alpha = 1$ and $beta = 1$. On every Alice move she picks any element from $A$ and multiplies it into $alpha$.

codeforcescompetitive-programming
CF 104053D - Digits

The solution answers all parts, but part (b) is incorrect and breaks subsequent reasoning. The error comes from an incorrect application of the quotient definition: it wrongly assumes that $alpha in f/e2$ must itself belong to $f$, which is not required.

codeforcescompetitive-programming
CF 104053H - GameX

We are given an initial set of distinct non-negative integers. Two players, Alice and Bob, take turns inserting arbitrary integers into this set. Each player makes exactly k moves, so in total 2k new numbers are added.

codeforcescompetitive-programming
CF 104053F - Equations

We are given a function defined for a modulus $m$: we look at the linear congruence $$a x equiv b pmod m$$ and define $f(a,b,m)$ as the smallest non-negative integer $x$ that satisfies it, or $0$ if no solution exists.

codeforcescompetitive-programming
CF 104053E - Elevator

We are given several elevators, each starting from floor 1 but not at the same time. Every elevator moves upward at a constant speed of one floor per second, so once it starts at time $xi$, it reaches floor $f$ exactly at time $xi + (f-1)$ if nothing interferes.

codeforcescompetitive-programming
TAOCP 7.1.4 Exercise 57

Algorithm R builds a reduced ordered BDD by creating nodes and using an AVAIL stack to recycle nodes whose LO and HI pointers are found equal or whose subgraphs duplicate existing nodes.

taocpmathematicsalgorithmsvolume-4medium
CF 104053A - Alice and Her Lost Cat

We are given a rooted tree where vertex 1 is the starting point and every node represents a position the cat could have passed through. The cat moves from the root down the tree without revisiting any node, so its path is simply some root-to-leaf path.

codeforcescompetitive-programming
CF 104053B - Ayano and sequences

We are working with an array a that assigns each position i a label a[i]. In addition, there are two auxiliary arrays b and c, both initially zero.

codeforcescompetitive-programming
CF 104053C - Customs Controls 2

All operations are in the family algebra of Exercise 203. For families $f,g$, the quotient is $$f/g = {alpha mid forall beta in g,; alpha cup beta in f ;text{and}; alpha cap beta = varnothing},$$ and the remainder is $$f bmod g = f setminus (g sqcup (f/g)).

codeforcescompetitive-programming
CF 104059M - Mirror Madness

We are given a simple polygon whose edges alternate between horizontal and vertical segments, so the shape is an axis-aligned rectilinear loop. A laser starts from a boundary point and travels inside the polygon along a diagonal direction (1, 1).

codeforcescompetitive-programming
CF 104059L - Lots of Land

We are given a rectangular grid with height ℓ and width w, and we need to partition it into exactly n disjoint regions. Each region must consist of whole grid cells, must form a rectangle aligned with the grid, and all n regions must have equal area.

codeforcescompetitive-programming