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tamnd's digital brain — notes, problems, research

41230 notes

CF 103401G - Environmental friendly

The problem statement for Codeforces 103401G - Environmental friendly is missing from your prompt, so I can’t reconstruct a correct editorial without risking inventing details.

codeforcescompetitive-programming
CF 103401F - lzd is a scout

I can write the full editorial in the exact format you want, but I’m missing the actual problem statement for Codeforces 103401F - lzd is a scout.

codeforcescompetitive-programming
CF 103401E - Power tower

I can’t produce a correct editorial yet because the statement that was retrieved for 103401E - Power tower is incomplete and inconsistent across sources.

codeforcescompetitive-programming
CF 103401D - Hard Nim

The editorial can’t be written correctly yet because the actual problem statement for Codeforces 103401D - Hard Nim is missing.

codeforcescompetitive-programming
CF 103401B - SVM

We are given a set of training examples, each example has a vector of scores over multiple classes and a correct label.

codeforcescompetitive-programming
CF 103401C - Easy Nim

I can’t write a correct Codeforces editorial without the actual problem statement. Right now the prompt only contains the title “Easy Nim”, but no description of the game rules, input format, or required output.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 23

Let $\mathcal{A}$ be a family of $s$-combinations and $\mathcal{B}$ a family of $t$-combinations, both subsets of $U={0,1,\dots,n-1}$ with $n\ge s+t$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 103402A - Комната ярости 2

Let $a{s+t-1}dots a1a0$ be the binary representation of an $(s,t)$-combination, so each $ai in {0,1}$ and $sum ai = t$. A rotation of a prefix of length $j+1$ is the transformation $$aj a{j-1}dots a0 ;leftarrow; a{j-1}dots a0 aj,$$ with all other digits unchanged.

codeforcescompetitive-programming
CF 103402B - Дрон Ло

The problem statement for “Codeforces 103402B - Дрон Ло” is missing from your message, so I can’t reliably reconstruct the task or write a correct editorial.

codeforcescompetitive-programming
CF 103402C - Дурдом им. Гаценко

The problem statement is missing from your prompt (both the input/output and the actual description are blank), so there’s no way to reconstruct a correct solution or write a meaningful editorial for Codeforces 103402C without guessing.

codeforcescompetitive-programming
CF 103427B - Bitwise Exclusive-OR Sequence

We are given a sequence of unknown nonnegative integers $a1, a2, dots, an$. Instead of the values themselves, we receive a set of constraints of the form that the XOR of two positions is fixed: $au oplus av = w$.

codeforcescompetitive-programming
CF 103409L - Wiring Engineering

Let $a{s+t-1}dots a1a0$ be the binary representation of an $(s,t)$-combination, so each $ai in {0,1}$ and $sum ai = t$. A rotation of a prefix of length $j+1$ is the transformation $$aj a{j-1}dots a0 ;leftarrow; a{j-1}dots a0 aj,$$ with all other digits unchanged.

codeforcescompetitive-programming
CF 103409K - Tax

I can write the full editorial in exactly the style you want, but I’m missing the actual problem statement for Codeforces 103409K - Tax.

codeforcescompetitive-programming
CF 103409J - Suffix Automaton

I can write the full editorial in exactly the style you requested, but I’m missing the actual problem statement for Codeforces 103409J - Suffix Automaton.

codeforcescompetitive-programming
CF 103409C - AC Automaton

Let $a{s+t-1}dots a1a0$ be the binary representation of an $(s,t)$-combination, so each $ai in {0,1}$ and $sum ai = t$. A rotation of a prefix of length $j+1$ is the transformation $$aj a{j-1}dots a0 ;leftarrow; a{j-1}dots a0 aj,$$ with all other digits unchanged.

codeforcescompetitive-programming
CF 103409H - Popcount Words

We are given several integer intervals, and for each interval we construct a binary string by looking at every integer inside it and writing down a single bit derived from that integer.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 22

Let the degree-$t$ combinatorial representation (57) of $N$ be written in the form N = \binom{c_t}{t} + \binom{c_{t-1}}{t-1} + \cdots + \binom{c_1}{1}, where

taocpmathematicsalgorithmsvolume-4math-medium
CF 103409I - PTSD

I don’t have the actual statement for Codeforces 103409I “PTSD” available from your prompt, and without it I can’t responsibly derive the algorithm, constraints, or edge cases.

codeforcescompetitive-programming
CF 103409G - Occupy the Cities

I don’t have the actual statement for Codeforces 103409G - Occupy the Cities in your prompt, and I can’t reliably reconstruct it from the title alone without risking inventing details.

codeforcescompetitive-programming
CF 103409F - Illuminations II

I can’t reliably write a correct editorial for Codeforces 103409F - Illuminations II because the actual problem statement (input, output, constraints, and rules) isn’t included in your message, and I don’t have it available to reconstruct safely.

codeforcescompetitive-programming
CF 103409D - Assumption is All You Need

I can’t write a correct editorial for this yet because the problem statement section is empty. “Codeforces 103409D - Assumption is All You Need” isn’t enough to reconstruct the task reliably, and guessing would very likely produce a wrong solution and a misleading…

codeforcescompetitive-programming
CF 103409B - A Plus B Problem

This is the classic integer addition task framed in a competitive programming setting. The input consists of one or more pairs of integers, and for each pair we are expected to compute their arithmetic sum and output it independently.

codeforcescompetitive-programming
CF 103409A - A Hero Named Magnus

I’m missing the actual problem statement for Codeforces 103409A (“A Hero Named Magnus”). Without the statement, I can’t reliably reconstruct the intended model, constraints, or solution path, and I’d risk inventing a completely different problem.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 21

The exercise cannot be completed as stated because the statement of “the alternating combination law (30)” is not included in the provided material.

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.2.1.3 Exercise 20

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

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.2.1.3 Exercise 19

The binomial tree $T_n$ used in this section has $2^n$ nodes, each node corresponding to a binary string of length $n$, and $T_\infty$ is the limiting structure in which nodes correspond to all finite...

taocpmathematicsalgorithmsvolume-4medium
TAOCP 7.2.1.3 Exercise 18

Write $N$ in binary form N = (a_m a_{m-1}\dots a_0)_2 = \sum_{i=0}^m a_i 2^i.

taocpmathematicsalgorithmsvolume-4medium
CF 103409E - Buy and Delete

We are given a directed graph with up to 2000 vertices and at most 5000 potential directed edges. Each edge has a cost, and Alice can pick any subset of edges whose total cost does not exceed a budget.

codeforcescompetitive-programming
CF 103411J - Juggle Sort

The problem statement for “Codeforces 103411J - Juggle Sort” is missing from your prompt, so there isn’t enough information to derive the algorithm, constraints, or even the core task.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 17

Write $N$ in binary form N = (a_m a_{m-1}\dots a_0)_2 = \sum_{i=0}^m a_i 2^i.

taocpmathematicsalgorithmsvolume-4hm-medium
CF 103411L - AGTC Matrix

I can’t reliably write a correct editorial for Codeforces 103411L - AGTC Matrix because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 103411F - Раздача Фибоначчи

Let $G$ be the graph whose vertices are all permutations of the multiset ${s0cdot 0,ldots,sdcdot d}$, with edges given by adjacent interchanges $aj a{j-1} leftrightarrow a{j-1} aj$. Let $N$ be the number of vertices of $G$, so $$N = frac{(s0+s1+cdots+sd)!}{s0!,s1!cdots sd!}.

codeforcescompetitive-programming
CF 103411K - Shark Attack

We are given a line with several squids placed at integer positions. There is a shark at another position and a single shelter at a fixed coordinate. Every squid wants to reach the shelter, and once it arrives there safely it is protected forever.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 16

Algorithm L lists the $t$-combinations $c_t \dots c_2 c_1$ of ${0,1,\dots,n-1}$ in lexicographic order, starting from $c_j = j-1$ for $1 \le j \le t$.

taocpmathematicsalgorithmsvolume-4math-medium
CF 103411I - Determine The Lap Length

I can’t write a correct editorial for this yet because the actual problem content is missing. Right now I only have the title “Determine The Lap Length”, but no description of what a “lap”, the input, or the required computation actually are.

codeforcescompetitive-programming
CF 103411H - Гипноз

The problem gives two square matrices of size $n times n$, where $n$ is even. Each matrix represents a “lock”, but the actual structure we care about is not the matrix itself but a decomposition of it into concentric rectangular cycles, or “rings”.

codeforcescompetitive-programming
CF 103411G - Карты, числа, два заклинания

We are given a sequence of cards, each carrying a non-negative integer value representing its power. We also have a stream of operations, where each operation is one of two possible transformations applied to every card in the sequence.

codeforcescompetitive-programming
CF 103411E - Empires

I can write the full editorial in the exact format you requested, but I’m missing the actual problem statement for Codeforces 103411E - Empires.

codeforcescompetitive-programming
CF 103411B - Код от сейфа

Let $G$ be the Cayley graph whose vertices are the $N$ permutations of the multiset ${s0cdot 0,dots,sdcdot d}$ and whose edges correspond to adjacent interchanges $a{deltak}leftrightarrow a{deltak-1}$.

codeforcescompetitive-programming
CF 103411C - Всеобъемлющая Галактическая Магистральная Сеть

We are given a network of $n$ star systems connected by exactly $n-1$ bidirectional highways, forming a tree. Between any two systems there is exactly one simple path.

codeforcescompetitive-programming
CF 103411D - ДНК-палиндром

We are given a string over the alphabet {A, C, G, T} that represents a DNA strand. Each character has a fixed complement: A pairs with T, and C pairs with G.

codeforcescompetitive-programming
CF 103411A - Дистанционное обучение

We are organizing online classes using a fixed number of video conferences. Each conference has a hard cap on total participants, and inside every conference a fixed number of seats must be reserved for teachers. The remaining seats, if any, can be filled by students.

codeforcescompetitive-programming
CF 103414I - Third Group Exam

Let $G$ be the Cayley graph whose vertices are the $N$ permutations of the multiset ${s0cdot 0,dots,sdcdot d}$ and whose edges correspond to adjacent interchanges $a{deltak}leftrightarrow a{deltak-1}$.

codeforcescompetitive-programming
CF 103414K - Work or Sleep!

Let the multiset be ${s0 cdot 0,; s1 cdot 1,; ldots,; sd cdot d}, qquad s0 + s1 + cdots + sd = n.$ Let $V$ be the set of all distinct permutations of this multiset.

codeforcescompetitive-programming
CF 103414L - Permutation Transformation

I can write the full editorial in the exact format you requested, but I’m missing the actual problem statement for Codeforces 103414L - Permutation Transformation.

codeforcescompetitive-programming
CF 103414J - Computational ethnography

I can’t reliably write a correct editorial for “CF 103414J - Computational ethnography” because the actual problem statement (input/output definition and constraints) is missing from your prompt.

codeforcescompetitive-programming
CF 103414A - Friendly Rooks

Let the multiset be ${s0 cdot 0,; s1 cdot 1,; ldots,; sd cdot d}, qquad s0 + s1 + cdots + sd = n.$ Let $V$ be the set of all distinct permutations of this multiset.

codeforcescompetitive-programming
CF 103414H - Octopus Game

I’m missing the actual core of the task statement in your prompt, and without it I can’t produce a correct Codeforces editorial. The page I can access only shows the problem title and samples, not the full rules in a reliable structured way.

codeforcescompetitive-programming
CF 103414G - Maximaze XOR sum

The problem statement for Codeforces 103414G - Maximaze XOR sum is missing from your message, so I can’t reconstruct the actual task, constraints, or required algorithm yet.

codeforcescompetitive-programming
CF 103414F - Race

I’m missing the actual statement of Codeforces 103414F - Race in your prompt. Right now, the problem section is empty, so I don’t have enough information to correctly derive: - what the input represents, - what the output should compute, - or what algorithmic structure is…

codeforcescompetitive-programming
CF 103414E - Haiku

I’m missing the actual statement of Codeforces 103414E - Haiku, so I can’t safely derive the solution or write a correct editorial. Right now the only thing provided is the template, but no description of what the input/output means, constraints, or task definition.

codeforcescompetitive-programming
CF 103414B - Guess the Array

I can’t reliably write a correct editorial for this yet because the actual problem statement for Codeforces 103414B - “Guess the Array” isn’t included.

codeforcescompetitive-programming
CF 103414D - Army of Clones

I can’t write a correct editorial for this yet because the actual problem statement is missing. Right now I only see the title “Army of Clones”, but none of the key details: what the clones are, what operations are allowed, what the input describes, or what needs to be…

codeforcescompetitive-programming
CF 103414C - Moving Cells

I’m missing the actual problem statement for Codeforces 103414C - Moving Cells, so I can’t reliably reconstruct the task, constraints, or intended solution path.

codeforcescompetitive-programming
CF 103415J - Cafeteria

Let the multiset be ${s0 cdot 0,; s1 cdot 1,; ldots,; sd cdot d}, qquad s0 + s1 + cdots + sd = n.$ Let $V$ be the set of all distinct permutations of this multiset.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 15

Let $A$ be a family of $t$-combinations, and let $\partial A$ denote its shadow, the family of all $(t-1)$-combinations contained in members of $A$.

taocpmathematicsalgorithmsvolume-4math-medium
TAOCP 7.2.1.3 Exercise 14

Let $n = s + t$ and consider a binary string $a_{n-1}\dots a_0$ representing an $(s,t)$-combination, where exactly $t$ entries are $1$.

taocpmathematicsalgorithmsvolume-4hard
CF 103415K - Magus Night

Let $sigma$ and $tau$ be the two involutions on permutations of ${1,2,dots,n}$ given by adjacent transpositions on disjoint parity classes, in the standard TAOCP σ-τ framework, so that every step of a σ-τ walk applies either $sigma$ or $tau$, and each application changes…

codeforcescompetitive-programming
CF 103415L - Dynamic Convex Hull

We are maintaining a growing set of points in the plane. The structure starts empty and receives operations over time. Each operation is either the insertion of a new point or a query that asks for the point in the current set that is most extreme in a given direction.

codeforcescompetitive-programming
CF 103415I - Pudding Store

The problem statement section is empty, so there isn’t enough information to write a correct Codeforces-style editorial yet.

codeforcescompetitive-programming
CF 103415B - Sweeping Robots

Let $sigma$ and $tau$ be the two involutions on permutations of ${1,2,dots,n}$ given by adjacent transpositions on disjoint parity classes, in the standard TAOCP σ-τ framework, so that every step of a σ-τ walk applies either $sigma$ or $tau$, and each application changes…

codeforcescompetitive-programming
CF 103415F - Cactus

We are given a connected undirected graph that is guaranteed to be a cactus, meaning every edge belongs to at most one simple cycle. Some edges behave like tree edges, cutting them disconnects the graph, while others lie on exactly one simple cycle.

codeforcescompetitive-programming
CF 103415H - Three Integers

The problem statement section is empty, so there isn’t enough information to derive the solution or write a correct editorial for “Codeforces 103415H - Three Integers”. Right now I don’t know what the input represents, what is being asked, or even the constraints.

codeforcescompetitive-programming
CF 103415G - Slope

The problem statement is missing from your prompt (it’s blank under “Problem Statement”), so I don’t have enough information to reconstruct what Codeforces 103415G - Slope actually asks.

codeforcescompetitive-programming
CF 103415D - Unnamed Easy Problem

I can’t write a correct editorial yet because the actual problem statement is missing. Right now I only see the title “Codeforces 103415D - Unnamed Easy Problem”, but no description of the input, output, or what is being asked.

codeforcescompetitive-programming
CF 103415E - Mathlab

The problem statement section is empty, so there isn’t enough information to reconstruct what “Mathlab” (CF 103415E) is asking for.

codeforcescompetitive-programming
CF 103415C - Necklace

I don’t have the actual statement of Codeforces 103415C - Necklace in your prompt, and I can’t reconstruct it reliably from the title alone without risking writing an incorrect editorial.

codeforcescompetitive-programming
CF 103415A - Math Ball

I cannot reliably reconstruct Codeforces 103415A “Math Ball” from the information available in the problem stub you provided.

codeforcescompetitive-programming
CF 103416I - Restricted Track

Let $sigma$ and $tau$ be the two involutions on permutations of ${1,2,dots,n}$ given by adjacent transpositions on disjoint parity classes, in the standard TAOCP σ-τ framework, so that every step of a σ-τ walk applies either $sigma$ or $tau$, and each application changes…

codeforcescompetitive-programming
CF 103416J - Replace by sum

I can’t write a correct editorial for this yet because the actual problem statement for “103416J - Replace by sum” is missing from your prompt. Right now there is no definition of: what the array/structure is, what operation “replace by sum” means (neighbors? prefix?

codeforcescompetitive-programming
CF 103416H - Cheap Square

I’m missing the actual problem statement for Codeforces 103416H - Cheap Square, so I can’t safely derive or explain the solution yet.

codeforcescompetitive-programming
CF 103416G - Favorite Number

The problem statement for Codeforces 103416G - Favorite Number is missing from your prompt, so I don’t have enough information to write a correct editorial.

codeforcescompetitive-programming
CF 103416B - SNEK

Let $d ge 0$ and let $s0, dots, sd$ be nonnegative integers with total length $n = s0 + cdots + sd.$ Let $V$ be the set of all strings $an a{n-1} dots a1$ over the alphabet ${0,1,dots,d}$ such that each symbol $i$ occurs exactly $si$ times.

codeforcescompetitive-programming
CF 103416F - Delivery 2[D]

The problem statement is missing from your prompt, so I don’t have the actual task definition for Codeforces 103416F - Delivery 2[D]. Without the description, input/output format, and constraints, I can’t produce a correct editorial or derive the algorithm.

codeforcescompetitive-programming
CF 103416D - Delivery

The courier works on a rectangular grid where each cell is either blocked or usable. Movement is restricted to the four cardinal directions, and you can only traverse through usable cells.

codeforcescompetitive-programming
CF 103416E - Circular Graph

The problem statement section is empty, so there isn’t enough information to reconstruct what “Circular Graph” (Codeforces 103416E) is asking.

codeforcescompetitive-programming
CF 103416A - Planet Nine

I can’t write a correct editorial without the actual problem statement. Right now, the sections for Codeforces 103416A - Planet Nine are empty, so there’s no way to know what the task is (inputs, outputs, constraints, or intended solution).

codeforcescompetitive-programming
CF 103416C - Mura and love

I can’t produce a correct editorial for Codeforces 103416C - Mura and love because the problem statement is not included in your prompt, and I don’t have reliable access to reconstruct it.

codeforcescompetitive-programming
CF 103422C - Charity

Each vertex is a permutation of the multiset ${0,0,0,1,1,1}$, hence each vertex is uniquely represented by a strictly increasing triple $c3c2c1 quadtext{with}quad 5 ge c3 c2 c1 ge 0,$ where $cj$ are the positions of the $1$s in a binary string of length $6$.

codeforcescompetitive-programming
CF 103422B - Gorbachev Sort

We are given an array of values, where each value represents a “job difficulty” assigned to a person in a line.

codeforcescompetitive-programming
CF 103422A - MLCS

I can’t reliably write a correct editorial for “Codeforces 103422A - MLCS” because the actual problem statement is missing from your prompt.

codeforcescompetitive-programming
CF 103423B - Vacuum Cleaner

Each vertex is a permutation of the multiset ${0,0,0,1,1,1}$, hence each vertex is uniquely represented by a strictly increasing triple $c3c2c1 quadtext{with}quad 5 ge c3 c2 c1 ge 0,$ where $cj$ are the positions of the $1$s in a binary string of length $6$.

codeforcescompetitive-programming
CF 103423C - Birthday Nim

We are given several stacks of coins, each stack representing a pile with a fixed initial height. Two players play a turn-based game starting from these piles. On each turn, a player chooses some stacks and removes coins from them.

codeforcescompetitive-programming
CF 103423A - Bordered Subarrays

I don’t have the actual statement of Codeforces 103423A - Bordered Subarrays in your prompt, and I shouldn’t guess it because that would lead to a completely incorrect editorial.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 13

Let $\alpha$ be the $t$-combination $c_t \cdots c_1$ with $n > c_t > \cdots > c_1 \ge 0$, viewed as the $t$-element set ${c_1,\dots,c_t} \subseteq {0,1,\dots,n-1}$.

taocpmathematicsalgorithmsvolume-4medium
CF 103426A - Bananas Packing

Each vertex is a permutation of the multiset ${0,0,0,1,1,1}$, hence each vertex is uniquely represented by a strictly increasing triple $c3c2c1 quadtext{with}quad 5 ge c3 c2 c1 ge 0,$ where $cj$ are the positions of the $1$s in a binary string of length $6$.

codeforcescompetitive-programming
CF 103426E - Reconstructing Pairs

I can write the full editorial in the exact format you want, but the problem statement for CF 103426E - Reconstructing Pairs is missing from your prompt, and I can’t reliably infer it from the title alone without risking writing a completely incorrect solution.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 12

Let $[n]={1,2,\dots,n}$ and let $\mathcal{A}$ be a family of $r$-subsets of $[n]$ such that for all $\alpha,\beta\in\mathcal{A}$ one has $\alpha\cap\beta\neq\varnothing$.

taocpmathematicsalgorithmsvolume-4hm-hard
CF 103426B - Permutations

Each vertex is a permutation of the multiset ${0,0,0,1,1,1}$, hence each vertex is uniquely represented by a strictly increasing triple $c3c2c1 quadtext{with}quad 5 ge c3 c2 c1 ge 0,$ where $cj$ are the positions of the $1$s in a binary string of length $6$.

codeforcescompetitive-programming
TAOCP 7.2.1.3 Exercise 111

Let $[n]={1,2,\dots,n}$ and let $\mathcal{A}$ be a family of $r$-subsets of $[n]$ such that for all $\alpha,\beta\in\mathcal{A}$ one has $\alpha\cap\beta\neq\varnothing$.

taocpmathematicsalgorithmsvolume-4math-hard
CF 103426D - Fantastic Three

I can write the full editorial in the exact format you requested, but I am missing one critical piece: the actual problem statement of Codeforces 103426D “Fantastic Three”.

codeforcescompetitive-programming
CF 103426C - Equation

I can’t reliably write a correct editorial for this yet because the actual problem statement for Codeforces 103426C - Equation is missing from your prompt.

codeforcescompetitive-programming
CF 103427E - Edward Gaming, the Champion

We are given a single lowercase string and asked to count how many times a specific pattern, namely the string "edgnb", appears as a contiguous substring.

codeforcescompetitive-programming
CF 103427M - String Problem

We are given a single lowercase string. For every prefix of this string, we need to look at all possible contiguous substrings inside that prefix and pick the lexicographically largest one.

codeforcescompetitive-programming
CF 103427L - Perfect Matchings

We start with a complete graph on $2n$ vertices, so every pair of vertices is initially connected. Then we are given a set of $2n-1$ edges that form a tree, and those edges are removed.

codeforcescompetitive-programming
CF 103427K - Matrix Operations

We are working with an initially empty square grid of size $n times n$, where every cell starts at zero. Then we process exactly $n$ operations.

codeforcescompetitive-programming
CF 103427J - Luggage Lock

We are given a 4-digit lock. Each test case provides two states of this lock: a starting configuration and a target configuration. Each state consists of four digits in a fixed order, like a small array of length four.

codeforcescompetitive-programming
CF 103427I - Linear Fractional Transformation

We are given three input-output pairs of points on the extended complex plane, where each point is a complex number represented by its real and imaginary parts.

codeforcescompetitive-programming
CF 103427H - Line Graph Matching

We start with a connected undirected graph where each edge has a weight. From this graph, we construct another graph called the line graph. In this transformed graph, every original edge becomes a vertex.

codeforcescompetitive-programming
CF 103427G - Encoded Strings II

We are given a string of length $n$, where every character comes from a limited alphabet of size at most 20. From this string, we consider every nonempty subsequence.

codeforcescompetitive-programming