Questions tagged [ds.algorithms]

Questions regarding well-defined instructions for completing a task, and relevant analysis in terms of time/memory/etc.

394 questions with no upvoted or accepted answers
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Is the dominating set problem constant-factor-approximable in undirected path graphs?

I am interested in the complexity of the minimum dominating set problem (MDSP) in some specific graph class. A graph is an undirected path graph if it is the vertex-intersection graph of a family of ...
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362 views

Efficiently approximating derivative of a well-behaved function

I need an algorithm for adaptive sampling a well-behaved function and computing its derivative in the sampling range with prescribed accuracy. The function has no more than one minimum in the sampling ...
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what is the best heuristic to solve 3AP with Euclidean costs?

As is well known, assignment problems for $n$-partite graphs, with $n$>2 are NP-hard, where as assignment problems on bipartite graphs can be solved in polynomial time using the Kuhn's Hungarian ...
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109 views

Efficient Enumeration and Parameterization of Graphs Deriving from Delaunay Tesselations in 3D

This is a repost from a question on Computational Science. No proper answer was found and it was suggested that TCS might be able to answer. So here it goes: Is there an algorithm that enumerates the ...
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2k views

Which algorithm can do a stable in-place binary partition with only O(N) moves?

I'm trying to understand this paper: Stable minimum space partitioning in linear time. It seems that a critical part of the claim is that Algorithm B sorts stably a bit-array of size n in O(...
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399 views

Type inference with subtype constraints and polymorphism using Trifonov and Smith's constraint maps

Trifonov and Smith's Subtyping Constrained Types (1996) introduces constraint maps to represent consistent closed constraint sets (such maps providing sets of lower and upper bounds to each variable ...
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127 views

Subgraph isomorphism on graph sequences

I'm looking for a subgraph isomorphism algorithm that takes advantage of properties of graph sequences. Say $\{G_i\}_{i=1}^k$ is a sequence of graphs on vertex set $\{1 ... n\}$, and two consecutive ...
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173 views

Tortoise and hare algorithms

Consider the problem: Given an array $a[0..n]$ where $n\ge 1$ and $a[i]\in [n]$ for all $i=0,\ldots,n$ find two indices $s\neq t$ so that $a[s] = a[t]$. This problem has a stunning solution running ...
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107 views

Consequence of Decision Tree Complexity of $k$-SUM Problem

Ezra and Sharir showed the $O(n^2\log^2 n)$ linear decision tree complexity for $k$-SUM problem [1], which improves the $O(n^3\log^3 n)$ complexity result of Cardinal et al [2]. It is known that $k$-...
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221 views

Integer queue summation

As part of a project I'm working on, we came up with an efficient algorithm for approximating the sum of an integers queue. The setting is as follows: Let $\epsilon>0$. we need to maintain a space-...
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145 views

Is 4-colors precoloring extension for planar graphs fixed parameter tractable?

Given a planar graph $G=(V,E)$, there exists a quadratic algorithms for 4-coloring $G$ (and $G$ is surely 4-colorable). Assume you are given a set of $k$ constraints of the form "$v_i \text{ is ...
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Explicit error bounds on the abelian hidden subgroup problem

What are some explicit forms for the error probability in the typical quantum abelian hidden subgroup algorithm as a function of oracles queries? Ettinger, Hoyer, and Knill give a result that the ...
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217 views

Is there a programming language where any arbitrary recursive function can be fused?

Compilers like GHC for Haskell use inlining as one of its most important optimising tools. Doing that is not possible for recursive functions, in general. A few techniques have been developed to amend ...
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325 views

Minimum length cuts needed to remove holes in a polygon

Suppose I'm given a connected polygon in the plane with holes. I can "remove" a hole by drawing a straight line from the boundary of a hole to another boundary (either of another hole, or the boundary ...
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181 views

Is the following “Occam's razor” decision problem a member of P?

While thinking about natural language processing, I came up with the following NP problem: OCCAM-k: Given a fixed natural number $k$, consider the following input: a natural number of states $S$ in ...
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110 views

Is there any known result for 1-median problem with negative weights in Euclidean space?

Given a set of $n$ points $v_1,\ldots,v_n$ in $R^d$, find a point $p$ such that $\sum_{i=1}^n w_i d(p,v_i)$ is minimized, where $w_i$ is the weight of $v_i$, which may be positive or negative. ...
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147 views

Lower bound for the maximal vectors problem

I am studying the (worst-case) complexity $C(n,d)$ required to solve the maximal vector problem: given a finite set $V$ of $n$ $d$-dimensional vectors, compute the set of undominated (a.k.a. skyline, ...
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2k views

Time complexity of standard semidefinite programming solvers

I am interested in exact scaling of the ellipsoid method and interior point methods for solving SDPs. (I am not interested in algorithms like multiplicative weights updates method.)
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705 views

Biconnected components of a directed graph?

I am looking for an algorithm for computing the biconnected components of a strongly connected directed graph.
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331 views

An algorithm to compute the number of paths of length at most k

So I had to answer the following question: Given a graph $G = (V, E)$, and two vertices $v_i, v_j$, compute the number of walks between $v_i$ and $v_j$ of length at most $k$. $G$ is not too large, ...
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213 views

Minimum weight expander

Expander constructions given an expander which is a sub-graph of a complete graph. Sometimes we don't want to construct an arbitrary expander, want to find an expander inside another given graph. In a ...
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243 views

How quickly can we find an arbitrary digit in multiplication?

In considering an answer to this question, I once again wondered how quickly we could find a digit in multiplication. We may first consider previous results. Finding the least significant digits is ...
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182 views

Testing the degree of a vertex

Let's say we have a graph $G$ with $n$ vertices. Given $\epsilon>0$ and a specific vertex $v$, consider the problem of deciding whether $\mathrm{deg}(v) < \frac{\epsilon}{3}n$ or $\mathrm{deg}(v)...
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112 views

Can one find good distance-2-separators in planar graphs?

It is known that planar graphs admit "good" separators, allowing to design PTASes for specific problems such as MINIMUM INDEPENDENT SET by recursive separation of the graph. However, it seems that ...
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Sparse graphs versus dense graphs

I am curious if there are graphs problems for which either - we know that time and/or space complexity is independent of graph sparsity we do not know whether or not graph sparsity can be exploited ...
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178 views

Scaling Algorithms for the Minimum Spanning Tree Problem?

In his paper "Scaling Algorithms for Network Problems", Harold Gabow details several algorithms for graph problems that work using scaling, iteratively refining a candidate answer by beginning with a ...
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98 views

Ref - Implicit selection made quick?

Given a matrix of size $n\times n$ with numbers, where every row is sorted, one can compute the $k$th smallest element in $O(n \log^2 n)$ time by simulating (implicitly) quick-select on this matrix (...
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149 views

log(OPT) approximation for directed balanced vertex separator

Leighton, Rao presented an $O(\log n)$ approximation algorithm for directed and undirected balanced vertex separator. Agarwal, Charikar, Makarychev, Makarychev improved this approximation factor of ...
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307 views

Good MCMC methods for exploring the space of independent sets

Let $G$ be an edge-weighted graph, and let (S, V-S) be a feasible pair if S is a maximal independent set. The weight of a feasible pair is computed by finding for each element of V-S the lightest edge ...
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376 views

Embedded dynamic programming (and planar subgraph isomorphism)

In Planar Subgraph Isomorphism Revisited, Frederic Dorn obtains an improved algorithm for Planar Subgraph Isomorphism, by using a technique he calls Embedded Dynamic Programming. This technique ...
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165 views

Finding the set of paths of smallest cumulated length that cover a given set of patterns

First of all, sorry for this long and maybe not very informative title... Context: Let $G=(V,E)$ be a directed graph, let $v_0 \in V$ be the initial node of paths that I will consider in the graph. ...
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2k views

Fast Hamiltonian Cycle finding Algorithm

We are struggling to understand a fast algorithm for finding Hamiltonian cycle (for random graphs) due to Prof. Alan Frieze* and see whether that algorithm could be implemented efficiently. If there ...
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158 views

Bottleneck $k$-link path in a complete DAG

Let $G$ be a complete DAG: It has vertices $v_1,\ldots,v_n$, and $v_iv_j$ is an edge if and only if $i<j$. Let $w(i,j)$ be the weight of the edge $v_iv_j$. The weight has the property that $w(i,j)&...
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127 views

Evaluating addition chains

I hope this is a suitable place to ask this question. An addition chain of size $n$ is a sequence $x_1, \dots, x_n$, where $x_1$ is fixed to 1 and $x_i = x_j + x_k$ for some $j,k < i$. I am ...
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426 views

Worst-case computational complexity of solving Diophantine equation

Manders and Adleman proved that the following decision problem is NP-complete: Given integers $a,b,c>0$, does the quadratic equation $ax^2+by-c=0$ have a solution in integers $x,y>0$? The ...
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168 views

Positive cut algorithm on bipartite graphs with negative weights

Let $G=(V,E,w)$ be a bipartite graph with weight function $w:E→\{-1,1\}$. Is there an efficient (polynomial) algorithm for finding some positive (not necessarily maximum) cut of $G$, if one exists? If ...
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163 views

Machine learning algorithms on hypergrap models

Graphical models are a very useful tool with many applications, whereby a joint distribution of a set of random variables is modeled using only pairwise dependencies between the variables, and two ...
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254 views

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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99 views

Lower bounds for randomized frequency estimation algorithms

Consider a stream of elements $s_1s_2\ldots s_N$. A counter-based frequency estimation algorithm uses $m$ counters and is required to answer queries of the form "How many times did $x$ appear"? It ...
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123 views

Is higher-order unification decidable for terms without abstractions within applications?

Consider the problem of higher order unification - that is, finding a substitution for the equation a = b, where a and ...
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170 views

Statistical Algorithms vs Convex Relaxations - Planted Clique

I am trying to understand exactly what the lower bounds for the query complexity of statistical algorithms imply for convex relaxations for the planted clique problem ? A recent paper by Feldman, ...
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93 views

Perfect hashing family variation - injectivity on $r$ disjoint sets

We denote by $[t]$ the set $\{1,2,\ldots,t\}$. A $(n,k)$-perfect hashing family is a set of functions $H=\{h_i:[n]\to[k]\}$ such that for every set $S\subset [n], |S|\leq k$, there exists some $h_S \...
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835 views

Best algorithm for inversion of symmetric positive-definite matrices

As I know, the time complexity for usual inversion algorithm of general matrix is $O(n^3)$. In recent years, there is a improvement from $O(n^3)$ to $O(n^{2.8....})$. However, does there exists a ...
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498 views

Generalized sequential machine synthesis subject to language equivalence/inclusion and reachability

A generalized sequential machine (GSM) is a generalization of a Mealy machine where on each transition one input symbol is read and 0 or more output symbols are written. As in a Mealy machine, we ...
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335 views

Bipartite vertex separator

Are there any common approaches for finding a vertex separator in a bipartite graph $G = (V_1, V_2, E)$ where the selected vertices are constrained to come from one partition of the graph? I have a ...
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164 views

Complexity of Roman numeral evaluation

I came up with a result the other day that arbitrary length Roman numeral evaluation can be modeled as a monoid: https://gist.github.com/4542999 1) Is this a known result? 2) If not, any ...
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1k views

Count $k$-hop neighborhood for every vertex

For a node $v$ of a directed unweighted graph $G$, I define the $k$-hop neighborhood of $v$ as the set of vertices that are reachable from $v$ in $k$ hops or fewer (that is following a path with $k$ ...
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188 views

Tree search guided by a probabilistic oracle

I'm trying to find a solution for the following problem. I have a tree $T$ of branching factor $b$ and depth $d$. For the moment, I only care about the case where I restrict $b=2$, but I would be ...
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283 views

k-uniform k-partite hypergraph matching in polynomial time

I have what seems like an elementary question, but google didn't throw up any answers for it. I would appreciate any pointers users here may provide. Please note that I have also asked this question ...
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450 views

Cheapest dissection of a grid polygon into rectangles with cost

My problem: Dissect a grid polygon into rectangles. (A grid polygon is a rectilinear polygon all of whose vertices have integer coordinates.) The rectangles must be taken from a predefined set (which ...

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