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tamnd's digital brain — notes, problems, research

41532 notes

CF 102890M - Mathematics society problem

We are given a number written as a string of digits and a set of deletion requirements that specify how many occurrences of each digit must be removed in total.

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CF 102890K - K contestants

We are effectively counting how many ways we can assemble a team of size k from two separate pools, where each pool contributes independently via combinations, but one pool is required to contribute at least c members.

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CF 102890I - Is this the best deal?

We are given three purchase amounts, denoted $t1, t2, t3$. There is also a function called discount(x) that tells us how much we actually pay if we buy something with nominal total value $x$.

codeforcescompetitive-programming
CF 102890G - Gold Fever

We are given a sequence of positions, each position representing a “state” with an immediate reward. From each position $i$, we are allowed to jump forward by a distance between two bounds $ai$ and $bi$, landing at some position $i + j$.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 40

Let $f_{l,m}(n)$ denote the number of partitions of $n$ having exactly $m$ parts and largest part equal to $l$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 102890F - Fit them all

We are given a packing problem on a fixed platform. The task is to determine how many cubes of increasing sizes we can place, starting from a cube of size 1×1×1 up to some largest size K×K×K, such that all of them fit on the platform under a specific placement rule.

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CF 102890E - End of the year bonus

We are given a circular line of people, each with a performance value. The bonus of each person depends on how their performance compares to their immediate neighbors on the left and right.

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CF 102890A - Acing the contest

We are dealing with a selection problem over three disjoint groups of students, which we can think of as three buckets of items labeled A, B, and C. Each group has a fixed number of students, and we want to form a team of exactly K students.

codeforcescompetitive-programming
CF 102891H - Ant MRT

We are given several ants placed at distinct points on a circular track of length (m). Each ant has a direction, either clockwise or counterclockwise, and they all move at unit speed. Whenever two ants meet, they instantly reverse direction.

codeforcescompetitive-programming
CF 102891D - Towers

The city is represented as a line of towers, each with a positive height. You are allowed to repeatedly perform a very specific operation: take one tower and move it onto an adjacent tower, merging them into a single tower whose height becomes the sum of the two.

codeforcescompetitive-programming
CF 102891B - Sphinx

We are given a line of numbered spheres placed from left to right in their natural order. Two agents repeatedly remove spheres from this line in a fixed alternating pattern until only one sphere remains.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 39

Let $f_{l,m}(n)$ denote the number of partitions of $n$ having exactly $m$ parts and largest part equal to $l$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 102893K - New Level

We are given a connected undirected graph with n vertices and m edges. Each vertex already has an integer label in the range 1 to k, and we are allowed to completely reassign these labels as long as we still use only values from 1 to k.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 38

Let $f_{l,m}(n)$ denote the number of partitions of $n$ having exactly $m$ parts and largest part equal to $l$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 102893G - Cooking

We are given a small collection of dishes, each of which must be prepared a fixed number of times. Cooking is done in pairs: on any day, the chefs choose two dishes, possibly the same one, and cook both together.

codeforcescompetitive-programming
CF 102894A - Big Brother Is Watching You

I don’t have the problem statement for Codeforces 102894A - Big Brother Is Watching You, so I can’t safely reconstruct the logic or write a correct editorial without guessing.

codeforcescompetitive-programming
CF 102896D - Down We Dig

The problem statement for Codeforces 102896D - Down We Dig is missing from your prompt, so there is nothing concrete to analyze or solve yet.

codeforcescompetitive-programming
CF 102896O - Optimum Server Location

The task can be interpreted as choosing the best node in a network of servers so that the total communication cost is minimized. The network forms a tree, meaning there are no cycles and exactly one simple path between any two nodes.

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CF 102896N - New Flat

I can’t write a correct Codeforces-style editorial for “102896N - New Flat” yet because the actual problem statement is missing.

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CF 102896J - Jumping Cat

I don’t have the actual problem statement for Codeforces 102896J - Jumping Cat in your prompt, and the editorial depends completely on the movement rules, input format, and what is being optimized or computed.

codeforcescompetitive-programming
CF 102896I - Interactive Knockout

I can’t reliably reconstruct Codeforces 102896I (“Interactive Knockout”) from the problem ID alone, and writing a correct editorial without the actual statement would risk inventing rules, which would make the whole solution useless.

codeforcescompetitive-programming
CF 102896G - Geometrical Combinatorics

I can write the full editorial in the exact format you requested, but I’m missing the actual problem statement for Codeforces 102896G - Geometrical Combinatorics.

codeforcescompetitive-programming
CF 102896E - Easy Measurements

We are given two independent water pumps and a combined measurement that links them in a slightly indirect way. Each pump has a constant rate: the first pump produces some integer amount of water over a fixed time window, and the second pump does the same over another window.

codeforcescompetitive-programming
CF 102896A - Almost Balanced Tree

We are asked to construct a binary tree with a fixed number of nodes, where every node is assigned a weight of either 1 or 2, matching given counts of each type. The structure must satisfy a balance condition defined locally at every node.

codeforcescompetitive-programming
CF 102896C - Color the Tree

I can’t reliably write an editorial for “Codeforces 102896C - Color the Tree” because the actual problem statement is missing here.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 37

Let $\lambda = (\lambda_1 \ge \lambda_2 \ge \cdots)$ and $\mu = (\mu_1 \ge \mu_2 \ge \cdots)$ be partitions of the same integer $n$ such that $\lambda \preceq \mu$ in the sense of majorization, that i...

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.2.1.4 Exercise 36

The Erdős–Lehner distribution (43) is the limiting distribution for the normalized random variable arising from the largest part (equivalently, the number of parts) of a random partition of $n$.

taocpmathematicsalgorithmsvolume-4hm-medium
CF 102896B - Brain-teaser

The task comes from a classic class of cryptoarithmetics where words represent numbers and each distinct letter is assigned a distinct digit from 0 to 9. Two given words are fixed as addends.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 35

The Erdős–Lehner distribution (43) is the limiting distribution for the normalized random variable arising from the largest part (equivalently, the number of parts) of a random partition of $n$.

taocpmathematicsalgorithmsvolume-4hm-medium
CF 102896M - Miser

We are given a timeline of days leading up to some event. On each day, a set of people arrives at a location and sees a sign showing a number.

codeforcescompetitive-programming
CF 102896L - Lookup Performance

We are given a fixed binary search tree whose nodes store integer keys. Each node also knows the minimum and maximum key inside its subtree, as well as the size of that subtree.

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CF 102896K - Kate's 2021 Celebration

We are given several packages of balloons sold by a store. Each package has a price and a multiset of digits written on its balloons.

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CF 102896H - Hit the Hay

The system describes a stochastic process that evolves over a short time horizon. A “baby” is always in one of three states, interpreted as awake, light sleep, and deep sleep.

codeforcescompetitive-programming
CF 102896F - Find a Square

We are given a collection of points on a 2D integer grid. The task is to determine whether it is possible to select four of these points that form the vertices of a square.

codeforcescompetitive-programming
CF 103964L - Huatuo's Medicine

Let $c1c2cdots cn$ be the part-count representation of a partition of $n$, so that $sum{j=1}^n j cj = n.$ The colex order on partitions corresponds to lexicographic order on the reversed vector $cn c{n-1}cdots c1$, so successive partitions are obtained by making the earliest…

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CF 103964F - The Battle of Guandu

I can’t write a correct editorial for this problem yet because the actual problem content is missing from your prompt (the statement section is empty).

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CF 102968I - Orchards

Stopped thinking

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CF 102968C - Ohara's Bits

We are given two sequences. The first sequence contains patterns, each pattern being a number that we interpret in binary. The second sequence contains numbers that are concatenated, in order, into a single long binary string with no separators.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 34

Let $S(n,m)$ denote the number of set partitions of ${1,\dots,n}$ into $m$ parts, so $S(n,m)=\left|\begin{matrix} n \ m \end{matrix}\right|$ in Knuth’s notation.

taocpmathematicsalgorithmsvolume-4hm-medium
TAOCP 7.2.1.4 Exercise 33

Let $S(n,m)$ denote the number of set partitions of ${1,\dots,n}$ into $m$ parts, so $S(n,m)=\left|\begin{matrix} n \ m \end{matrix}\right|$ in Knuth’s notation.

taocpmathematicsalgorithmsvolume-4hm-medium
CF 103964K - Game Rooms

The problem statement for Codeforces 103964K - Game Rooms is not included in your prompt (it only shows a placeholder with empty Input/Output sections). Without the actual rules of the problem, any “editorial” would be guesswork and would very likely be wrong.

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CF 103964J - Walk Around The Campsite

The task can be understood in geometric terms. Imagine a campsite drawn on a grid where some cells are occupied by tents or structures and the rest are empty ground.

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TAOCP 7.2.1.4 Exercise 32

Let $p(m)$ denote the number of partitions of $m$ in the sense of Section 7.

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CF 102968J - Pyra, Pyra, Pyraminx!

We are given a scrambled configuration of a Pyraminx, which is a tetrahedral twisty puzzle. Each test describes the full visible state of the puzzle as four triangular faces, each face being shown as a 1-3-5 triangular grid of colored stickers.

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CF 102968G - Complete Journey

We are given an undirected connected graph where every edge has a distinct weight, interpreted as “beauty”. Between any two vertices, you do not get to pick an arbitrary path in the usual sense.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 31

Let $\left| \begin{matrix} n \ k \end{matrix} \right|$ denote the number of partitions of $n$ into exactly $k$ parts, equivalently the number of partitions of $n$ whose Ferrers diagram has $k$ rows.

taocpmathematicsalgorithmsvolume-4math-medium
CF 102911G - Gamer Girl Gauntlet

I don’t have the actual statement of Codeforces 102911G - Gamer Girl Gauntlet in your prompt, so I can’t reliably reconstruct the logic or write a correct editorial without risking hallucination.

codeforcescompetitive-programming
CF 102911L - L Textiles

A clutter on the ground set $[n]={0,1,dots,n-1}$ is an antichain in the Boolean lattice: if $alpha,betain C$ and $alphasubseteqbeta$, then $alpha=beta$. Let $Mt$ be the number of sets in $C$ of size $t$, so that $(M0,M1,dots,Mn)$ is the size vector.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 30

Let $m \ge 1$ and $n \ge 0$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 102911A - Academic Recovery

A clutter on the ground set $[n]={0,1,dots,n-1}$ is an antichain in the Boolean lattice: if $alpha,betain C$ and $alphasubseteqbeta$, then $alpha=beta$. Let $Mt$ be the number of sets in $C$ of size $t$, so that $(M0,M1,dots,Mn)$ is the size vector.

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CF 102911H - Heavy Sort

Before writing the full editorial, there is a structural problem: the problem statement for Codeforces 102911H - Heavy Sort is missing from your prompt.

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CF 102911E - Experiment!

I can’t write a correct editorial for Codeforces 102911E - Experiment! without the actual problem statement. Right now the prompt contains only the template, so there’s no information about: what the input represents, what needs to be computed, or even the core operation…

codeforcescompetitive-programming
CF 102911D - Dancing Queen

We are given the integers from 1 to N, and we want to split them into two groups, call them Alice and Bob. The value contributed by each integer is exactly its numeric value, so if Alice receives a set of numbers, her total score is the sum of those numbers, and Bob’s score…

codeforcescompetitive-programming
CF 102911C - Chocolate Game: Love is War

The problem statement section is empty, so there isn’t enough information to reconstruct what “Chocolate Game: Love is War” actually asks. To write a correct Codeforces-style editorial, I need at least the rules of the game, input/output format, and constraints.

codeforcescompetitive-programming
CF 102904J - Черные и белые

The problem statement for Codeforces 102904J (“Черные и белые”) is not included in your prompt, so I cannot safely reconstruct the full editorial yet.

codeforcescompetitive-programming
CF 102904I - Подсчет операций

I can’t write a correct editorial yet because the problem statement for Codeforces 102904I - “Подсчет операций” is not available from the information provided, and I should not guess its rules or operations.

codeforcescompetitive-programming
CF 102904F - Exercise

Let $a1 ge cdots ge an ge 0$ and $a'1 ge cdots ge a'n ge 0$ be partitions of $n$, padded with zeros to length $n$.

codeforcescompetitive-programming
CF 102904G - Лемурьи вечеринки

We are given a line of lemurs, each with a distinct height. The lemurs are currently arranged in some arbitrary order, not sorted by height.

codeforcescompetitive-programming
CF 102904H - Дом в дереве

I can’t write a correct Codeforces editorial without the actual problem statement. “102904H - Дом в дереве” only gives the title, and that’s not enough to reconstruct the task reliably.

codeforcescompetitive-programming
CF 102904E - Мосты

I can write the full editorial in the requested Codeforces style, but I’m missing the actual problem statement for Codeforces 102904E - “Мосты” in your prompt.

codeforcescompetitive-programming
CF 102904C - Электронный замок

I’m missing the actual problem statement (the Input/Output and description are empty), so I can’t reliably reconstruct what “Электронный замок (Electronic lock)” is asking or derive a correct solution.

codeforcescompetitive-programming
CF 102904A - Coins

I can’t safely write a correct editorial for “Codeforces 102904A - Coins” yet because the identifier you provided does not correspond to a single stable Codeforces problem statement, and different sources map similar “Coins” titles to entirely different tasks.

codeforcescompetitive-programming
CF 102897G - New Game

Let $C subseteq mathcal{P}({0,1,dots,n-1})$ be a clutter, meaning that no two distinct sets in $C$ are comparable under inclusion. Let $Mt$ denote the number of $t$-element sets in $C$.

codeforcescompetitive-programming
CF 102897M - XCPCIO Board CLI Hard

We are given a simulation of a programming contest where many teams submit solutions to several problems over time. Each submission happens at a timestamp and either solves a problem (AC) or fails (WA).

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 29

Let $A_k(n)$ denote the Hardy–Ramanujan–Rademacher coefficient defined in equation (34) of Section 7.

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.2.1.4 Exercise 28

Let $A_k(n)$ denote the Hardy–Ramanujan–Rademacher coefficient defined in equation (34) of Section 7.

taocpmathematicsalgorithmsvolume-4hm-project
TAOCP 7.2.1.4 Exercise 27

Let $f(x)=e^{-x^{2}/n}, \qquad n>0.$ The Poisson summation formula in the form used in TAOCP states that for sufficiently rapidly decreasing $f$, $\sum_{k=-\infty}^{\infty} f(k)=\sum_{m=-\infty}^{\inf...

taocpmathematicsalgorithmsvolume-4hm-medium
TAOCP 7.2.1.4 Exercise 26

Let $f(x)=e^{-x^{2}/n}, \qquad n>0.$ The Poisson summation formula in the form used in TAOCP states that for sufficiently rapidly decreasing $f$, $\sum_{k=-\infty}^{\infty} f(k)=\sum_{m=-\infty}^{\inf...

taocpmathematicsalgorithmsvolume-4hm-medium
CF 102897E - BM 充饥

A partition of $n$ in part-count form is a vector $c1,dots,cn$ satisfying $c1+2c2+cdots+n cn=n,$ where $ck$ is the number of parts equal to $k$.

codeforcescompetitive-programming
CF 102897L - 咆哮

There are two enemy forces, each with its own health pool and a fixed per-round damage value. Time progresses in discrete rounds, and in round $i$, the player is forced to use exactly $i$ attack power in total, and all of it must be directed to exactly one of the two enemies.

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CF 102897H - Hsueh- Draw Progress

The task is to render a command line progress indicator for multiple scenarios. Each scenario describes a total amount of work and how much of it is already completed.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 25

Let P(q)=\prod_{k=1}^{\infty}(1-q^k)^{-1}, \qquad q=e^{-t}, \quad t>0.

taocpmathematicsalgorithmsvolume-4hm-hard
TAOCP 7.2.1.4 Exercise 24

Let E(z)=\prod_{k=1}^{\infty}(1-z^k), \qquad P(z)=\frac{1}{E(z)}=\sum_{n\ge 0} p(n)z^n.

taocpmathematicsalgorithmsvolume-4math-hard
CF 102897K - Kwords Find Kth Element

We are given several independent arrays. Each array contains integers, and across all arrays the total number of elements is at most one hundred thousand. After reading these arrays, we process a sequence of queries.

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CF 102897J - 大扫除

We are given several independent building descriptions. Each building consists of multiple floors, and each floor is represented by a string. Characters in the string describe whether a position contains trash and what type it is.

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CF 102897I - BM 旅游

We are given four large integers. Each integer is not directly the object of interest. Instead, each one encodes whether a particular sightseeing location has been visited.

codeforcescompetitive-programming
CF 102897D - Palindrome Hard Problem

We start with a collection of $n$ strings, all having the same length $m$, and only lowercase letters. The allowed operations let us repeatedly reduce the number of strings by either merging two strings in a few different ways or discarding one string entirely.

codeforcescompetitive-programming
TAOCP 7.2.1.4 Exercise 23

Let E(z)=\prod_{k=1}^{\infty}(1-z^k), \qquad P(z)=\frac{1}{E(z)}=\sum_{n\ge 0} p(n)z^n.

taocpmathematicsalgorithmsvolume-4hm-medium
CF 102897F - kita 买礼物

We are given a collection of coin types. Each type has a fixed denomination and a limited supply. From these coins, we want to know how many distinct total sums we can form using any combination of coins, but only considering totals from 1 up to m.

codeforcescompetitive-programming
CF 102897A - XCPCIO Board CLI Easy

We are simulating an online programming contest scoreboard that evolves over time as submissions arrive. Each submission belongs to a team, targets a problem, arrives at a timestamp, and is either accepted or rejected.

codeforcescompetitive-programming
CF 102897B - BM 算日期

We are given a starting year and an integer shift. The shift is applied to the year, but the result is not used directly.

codeforcescompetitive-programming
CF 102897C - BBpigeon Counting Trees

We are given a rooted tree structure indirectly, not by edges, but by a list of depths for each node. Node 1 is fixed as the root, and every node i comes with an integer ai describing how far it is from the root in terms of number of nodes on the path, including itself.

codeforcescompetitive-programming
CF 102898E - Yet Another Minimax Problem

We are given a collection of numbers, and we are asked to repeatedly combine them in a structured way until only one value remains.

codeforcescompetitive-programming
CF 102898A - Snowman

Let $U$ denote the set of all multicombinations $dt ldots d2 d1$ satisfying (6), that is $$s ge dt ge cdots ge d2 ge d1 ge 0.$$ The complement operation described in the hint is the standard involution on $U$ induced by reversal and complementation with respect to $s$.

codeforcescompetitive-programming
CF 102898D - Digidivisible Numbers

I can’t write a correct editorial for “Codeforces 102898D - Digidivisible Numbers” without the actual problem statement. The title alone isn’t enough to reliably reconstruct the task, and guessing would almost certainly produce a wrong solution and misleading reasoning.

codeforcescompetitive-programming
CF 102898C - Garbage Robot

I don’t have the statement of Codeforces 102898C - Garbage Robot available in my context, and I shouldn’t guess the problem details because that would produce a misleading editorial.

codeforcescompetitive-programming
CF 102898B - Teacher Sorting

I’m missing the actual problem statement for Codeforces 102898B - Teacher Sorting. Right now you’ve provided the editorial format, but not the key part that defines: what the input is, what transformation is required, and what must be output.

codeforcescompetitive-programming
CF 102899M - KK 与二叉树

We are given multiple test cases. Each test case describes a binary tree only through two traversal orders: a preorder sequence and a postorder sequence. All node values are distinct, so each sequence is a permutation of the same set of integers.

codeforcescompetitive-programming
CF 102899L - KK 学五子棋

Let $U$ denote the set of all multicombinations $dt ldots d2 d1$ satisfying (6), that is $$s ge dt ge cdots ge d2 ge d1 ge 0.$$ The complement operation described in the hint is the standard involution on $U$ induced by reversal and complementation with respect to $s$.

codeforcescompetitive-programming
CF 102899K - KK 与线代

We are given a fixed 4×4 matrix where every entry is constant except for one position that depends on an integer variable $x$. For every integer $x$ in the range $[l, r]$, we evaluate the determinant of this matrix and are asked to find the minimum value over the entire range.

codeforcescompetitive-programming
CF 102899J - KK与英语

We are given a single line of text representing a sentence that may contain the word “is” in different contexts.

codeforcescompetitive-programming
CF 102899C - KK 算日期

Let $n ge m ge 1$ and let $a1 ge a2 ge cdots ge am ge 1$ be a partition of $n$ such that $ Indeed, if $a1$ is the maximum part and $am$ is the minimum part, the condition gives $a1 - am le 1$, hence $am in {a1, a1 - 1}$. Therefore every part equals either $a1$ or $a1 - 1$.

codeforcescompetitive-programming
CF 102899H - KK 与十佳

We are given a list of integers representing scores assigned by judges. All values are nonzero and all are distinct. We are allowed to remove exactly one of these numbers. After removing it, we multiply all remaining numbers together, and that product becomes the final score.

codeforcescompetitive-programming
CF 102899I - KK 买股票

We are given a sequence of stock prices over n days. On each day i, the stock has a known price p[i]. KK is allowed to perform at most one complete transaction: he may buy once on some day and later sell once on a strictly later day.

codeforcescompetitive-programming
CF 102899G - KK 看跳舞

We are given multiple test cases. Each test case describes a sequence of $n$ distinct integers, which is a permutation of $1 ldots n$. The sequence represents the order in which dancers pass in front of an observer.

codeforcescompetitive-programming
CF 102899F - KK 与刷题

We are given a sequence of days, and on each day kk records how many wrong answers (WA) he made. These values form an array a[1..n]. Starting from a score of zero, the score evolves day by day. When processing day i, we compare the WA count a[i] with every previous day j < i.

codeforcescompetitive-programming
CF 102899D - KK 与卡牌

We are given two collections of heroes represented as cards. Each card has a short name, a string of lowercase letters, and a strength value written as a decimal number.

codeforcescompetitive-programming
CF 102899E - KK 与答辩

We are given several independent test cases. In each test case, there are multiple “defense sessions”. In every session, a list of students appears, and each student has a combined score computed as the sum of two components.

codeforcescompetitive-programming
CF 102899B - KK 学几何

We are given a stream of geometric figures, each described by a type identifier followed by its dimensions. Every figure contributes an area, and the task is to accumulate the total area across all figures and output the final sum rounded to one decimal place.

codeforcescompetitive-programming
CF 102899A - KK 画猪

The task is intentionally minimal: the program receives a single token on standard input and must respond with a fixed ASCII drawing of a pig.

codeforcescompetitive-programming