# Questions tagged [sorting]

Given a sequence of elements, find a permutation such that the elements are in a certain order.

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### Calculate sorting function complexity

I want to know which sorting technique is used in torch.sort: Quicksort, Introsort, Insertion sort or Selection sort ... because I need to calculate its complexity and thank you.
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### Low-Treewidth Sorting Networks

It was previously asked if there exist Boolean circuits of treewidth $O(\log n)$ that compute the majority function $\text{MAJ}_n$ on $n$ inputs. While a construction using online algorithms and the ...
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### Finding top-K items in a sliding window

Imagine we have a stream of bank transactions. Each transaction has a target account and some amount of money. I'd like to find top K accounts over some period of time (e.g. last 7 days) which ...
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### What would be the performance properties of a comb or shell sort where the gap sequence is the prime numbers?

In particular, the genesis of this idea was the notion that you could minimize the number of passes through the list in a comb sort by using the primes as a way to guarantee that every element gets ...
106 views

### A sorting algorithm that uses the minimum comparasions possible

I'm looking for a sorting algorithm that minimizes comparisons instead of time complexity. The algorithm shouldn't compare any two elements for which the relation between them can be derived from ...
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### Computing and maintaining the minimum of a set $S$ of integers while allowing updates on $S$

This question is about computing and maintaining the minimum of a set $S$ of integers while allowing updates on $S$. The computation model we are considering is the unit-cost RAM machine with linear ...
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### Sorting with an average of $\mathrm{lg}(n!)+o(n)$ comparisons

Is there a comparison-based sorting algorithm that uses an average of $\mathrm{lg}(n!)+o(n)$ comparisons? Existence of a worst-case $\mathrm{lg}(n!)+o(n)$ comparison algorithm is an open problem (...
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### Lower bound for reversing a list using queues

How do you prove (or disprove) that a list of length $n$ cannot be reversed in time $o(n \log n)$ using $O(1)$ queues? Each queue is FIFO. Time refers to the number of operations on the queues. ...
462 views

### Sorting a programs instructions until it works

Lets say I have a computer program below. (define (factorial x) (if (= x 0) 1 (else (* x (factorial (- x 1))))) I then take each line of the ...
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### Computing topological sort while keeping edges "short"

Motivation: I want to compute a topological sort order in which the connected vertices are close to each other. Problem statement: Given a DAG $G(V,E)$ with $n$ vertices, compute a topological sort ...
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### Does any DAG can be topologically sorted? [closed]

I am not good enough in computer science. My intention is to solve some programming problem in terms of DAG's. The key point is that before getting them into database, I need run "topological sort" in ...
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### Is sorting $n$ real numbers in time $O(n \sqrt{\log n})$ and linear space possible?

In the recent preprint https://arxiv.org/abs/1801.00776, it is claimed that $n$ real numbers can be sorted in time $$O(n \sqrt{\log n}),$$ and linear space. The paper seems reasonable, though I am ...
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### How fast can we sort a list if we know how it was written?

Let $G$ be a linear time (deterministic) turing machine that takes positive integers $n$ in unary to lists of length $n.$ For any fixed such $G$, define sparse-sort(G,n) as the problem of sorting the ...
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### Necessary and sufficient number of comparisons by every element to fully sort a set of n elements? [duplicate]

Given $n$ distinct elements. Is there a sorting algorithm which ensures that every element is compared atmost $\lg n$ time? Or is there a higher lower bound?
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### "Almost sorting" integers in linear time

I am interested in sorting an array of positive integer values $L = v_1, \ldots, v_n$ in linear time (in the RAM model with uniform cost measure, i.e., integers can have up to logarithmic size but ...
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### Original reference for Huffman shaped Merge Sort?

What is the first publication of the concept of optimizing merge sort by identifying sequences of consecutive positions in increasing orders (aka runs) in linear time; then repeatedly merging the ...
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### Enumerating topological sorts of a vertex-labeled DAG

Let $G = (V, E)$ be a directed acyclic graph, and let $\lambda$ be a labeling function mapping each vertex $v \in V$ to a label $\lambda(v)$ in some finite alphabet $L$. Writing $n := |V|$, a ...
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### Quick-select contiguous subarray

Motivated by the question from this blog post, the following data structure question seems interesting and fun to me. Preprocess: A list of numbers $A = a_1,...,a_n$ Query(s,t,k): Return the $k$-th ...
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### Quicksort: compute the expected number of comparisons as a function of $M$ and $t$

I stumbled upon this problem on a list of open problems in the analysis of algorithms dating back to 1997. Is it still open? Can anyone point to a reference with a full or partial solution, or at ...
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### Quicksort optimal partition

Has the question been studied, how to find the shortest sequence of partition choices so that a quick-sort algorithm can sort a set? To be clear, I'm not interested in quick sort per se, but in ...
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### Most efficient inplace merge algorithms (stable and unstable)

I am currently researching the best algorithms available to achieve an inplace merge operation: consider two consecutive sorted arrays of size n and ...
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### Sorting sequence with $O(n^{\frac{3}{2}})$ inversions

There is given sequence $a_1,...a_n$ such that there are $O(n^{\frac{3}{2}})$ inversions in this sequence. I am thinking about sorting algorithm for that. I know lower bound for number of ...
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### Determining what can be achieved by a permutation of elements of a noncommutative group

Fix a finite group $G$. I am interested in the following decision problem: the input is some elements of $G$ with a partial order on them, and the question is whether there is a permutation of the ...
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### Sorting using ring operations

Sorting is in $\mathsf{NP}$. Given a sorted list, it is trivial to check sortedness in linear time. Is there any evidence sorting of elements from an ordered gcd domain(eg: $\Bbb Z$) cannot be done ...
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### Are there any algorithms that are similar to Fagin's Algorithm, but for unranked lists?

Fagin's Algorithm is a popular algorithm for finding the top-$k$ items from multiple ranked lists of the items (i.e., via different scoring functions), using some monotonic aggregation function for ...
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### Reducing sorting to max-flow

Is there a linear-time reduction from the sorting problem to the max-flow problem? If so, what would such a reduction look like?
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### Is it enough to sort for polynomially many 0-1 sequences for a sorting network?

The 0-1 principle says that if a sorting network works for all 0-1 sequences, then it works for any set of numbers. Is there an $S\subset \{0,1\}^n$ such that if a network sorts every 0-1 sequence ...
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### Probabilistic sorting given pairwise comparison probability

Let $X = \{x_1, \dots, x_n\}$ be a set, and $f:[1..n]^2 \to [0, 1]$ be a function, such that $$f(i, j) \cdot f(j, k) \le f(i, k)$$ For all $1 \le i, j, k \le n$. Does there exist a randomized ...
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### Efficient recognition of sequences sortable by transpositions?

While reading the post, Probability of generating a desired permutation by random swaps, by Aaronson, I got interested in restricted sorting problem: If we restrict sorting algorithms to use ...
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### Is it possible to find the median with a linear size sorting network?

Is there a sorting network that makes only $O(n)$ comparisons and finds the median? The AKS sorting network sorts with $O(\log n)$ parallel steps, but here I am only interested in the number of ...
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### How to Quantify Entropy in a Data Set

I'm currently creating a program in Java to analysis the pathological cases of Quicksort. Namely, the transition of complexity from O(n^2) to O(nlogn) as a data set gets less ordered. Since Quicksort ...
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### Algorithm to merge two incomplete sequences of symbols (strings) into a complete one

I initially considered this problem trivial, but then looked with more attention, I could not find an easy solution. Let's say we have two ordered lists of symbols (strings): ...
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### What's the difference between "adaptive sorting" and "sorting almost sorted data quickly"?

A SIGMOD 2014 paper from Microsoft Research states that the "importance of sorting almost sorted data quickly has just emerged over the last decade", and goes on to propose variants of Patience sort ...