Questions tagged [space-complexity]

Asymptotic analyses of the space needed to run algorithms.

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Storing a configuration of nondeterministec machines in log space

In Sipser's book page 351: Recall that Savitch's theorem shows that we can convert nondeterministic TMs to deterministic TMs and increase the space complexity $f(n)$ by only a squaring, provided ...
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Proving inexistence of a PCOMPLETE language in log logarithmic space cannot exist

Hello and thank you for helping me understand the following: I am trying to understand why the following cannot exist: A P-Complete language in regards to a log-logarithmic space. context: Defining ...
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25 views

How will I calculate the time and space complexity for this pyramid algo? [duplicate]

This is an algo. programmed for displaying a letter pyramid if the buildPyramids() method is passed argument str, i.e. "12345": ...
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Existence of a P-Complete language with space($\log\log n$) reduction

I have been reading and searching and I still cannot understand if there exists a language as following: Can a language be P-complete with respect to $\mathsf{Space}(\log \log n)$ reductions? ...
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Understanding an example of an EXP-SPACE Problem

I am trying to understand the example given here of an EXP-SPACE time decision problem. They write : An example of an EXPSPACE-complete problem is the problem of recognizing whether two regular ...
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1answer
51 views

PSPACE-completeness of DFA intersection problem

Let some deterministic finite automata be given. There is a problem of determining whether the intersection of these DFA is empty, and I want to show its PSPACE-completeness. It seems to me that I ...
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Algorithm to Find $x$ and $y$ for array of $3n$ numbers such that 1/3 are less than $x$. 1/3 between $x$ and $y$ and 1/3 greater than $y$

We have An array of $3n$ elements. we want to Find $x$ and $y$ for array of $3n$ numbers such that 1/3 are less than $x$. 1/3 between $x$ and $y$ and 1/3 greater than $y$. We can solve this problem of ...
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PSPACE-hardness of the unbounded puzzle

Given a board of size $n \times 1$ where $n=\infty$ (basically a tape, one way infinite), and a set of colors $C$, some starting color $c_{start} \in C$, a set of templates $T$ in a form $(c_k, i, c_i,...
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1answer
60 views

Given a boolean matrix A of size n, A^p can be computed in space O(log n log p)

The solution to this problem can be found here. It says: To multiply $k$ matrices, we generate the result entry by entry, by running a counter $t$ and generating the $it$th entry in the product of ...
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3answers
132 views

Does White never lose in Chess if Chess is solved?

If the machine has enough memory and speed as to compute all states of the Chess game in a reasonable time, can a player with the white pieces - operated by a machine - lose a game?
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Showing that a directed graph that has a cycle belongs to NL [closed]

DCG = { G | Directed graphs that contains a cycle } How can I proof that DCG belongs to NL?
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26 views

The space complexity of a function that allocates space based on the input value and not size

What is the space complexity of the following hyphotetical function: void function(int n) { int[] array = new int[n]; // allocate array of size n return; } ...
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38 views

What is the complexity of finding e^(A) for a Hermitian matrix A?

If A is a hermitian matrix of size NxN .What is the order of no. of steps required to compute e^(A).How to prove it?
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Space complexity for storing integers in Python

So I was watching this mock interview by an Airbnb engineer on interviewing.io (https://youtu.be/cdCeU8DJvPM?t=1224) and around ~20:11 seconds he raises an interesting point. The question that the ...
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Why is $DSPACE(\log(n)) = NSPACE(\log(n))$ not known?

Here $DSPACE(\log(n))$ is the family of algorithms for which there exists a deterministic Turing machine using $O(\log(n))$ space. On the other hand $NSPACE(\log(n))$ is the family of algorithms for ...
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Is there any general, theoretical limit to time - space tradeoff?

In many algorithms, one can spot that improvements in time often are occupied by more memory requirements. For example usage of cache allows to speed up calculations by saving results in memory. Is ...
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57 views

Is the power of a natural number logspace-computable?

Given a constant $n\in\mathbb{N}_+$, is the simple power function $$ λ\,x\in\mathbb{N}_+.\,x^n $$ logspace computable by a logspace transducer (which has a read-only input tape, a working read-write ...
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Are polynomials in one variable logspace-computable?

Given a polynomial function $$p\quad=\quad \lambda\, x\in\mathbb{N}_0.\ \sum_{i=0}^n a_i x^i$$ with $a_i\in\mathbb{Z}$ for all $i\leqslant n$, can you compute $p$ by a logspace transducer if the input ...
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35 views

Space efficient representation of Regular graphs

Let $G$ be a $k$-regular graph (each vertex have a degreee $k$). It is trivial to store the graph in $O(\log n)$ space or words such that $j$th neighbour of any vertex can be found in $O(\log n)$ time....
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LogSpace reductions vs. PTime reductons for defining PSpace-completeness [closed]

Continuing Is every PSPACE-complete problem complete with respect to logspace reductions? : earlier, PSPACE-completeness was defined via logspace reductions (e.g., cf. http://www.cs.cornell.edu/~kozen/...
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Is Space Complexity Always Less Than Or Equal To Time Complexity?

Background I am working on proving a novel problem to be P-Complete, and this requires using a logspace reduction to reduce some known P-Complete problem to the novel problem. Particularly, I am ...
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66 views

Why log-space reduction is used for NL-completeness while PSPACE reduction isn't used for PSPACE completeness?

NL-Complete languages are defined by Log-space reduction, while PSPACE complete languages are defined by poly-time many-to-one reduction. According to these posts : Why not polynomial-space ...
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How is the problem, {⟨G⟩|G has no triangle} in Logspace?

I read this problem as a part of my course curriculum, in my professor's notes. I am not able to understand about the standard solution, that if I list all the possible triplets of vertices as 3-...
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What are some decidable problems which cannot be solved in real life(due to time and memory constraints)?

The first line of Sipser book for the Chapter- 'Time complexity', says that: Even when a problem is decidable and thus computationally solvable in principle, it may not be solvable in practice if the ...
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Maximum space consumption of stack and queue for DFS and BFS

I'm trying to determine the maximum memory consumption of the "pending nodes" data structure (stack/queue) for both travelings: BFS and (preorder) DFS. Since BFS and DFS while traveling graphs have ...
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1answer
34 views

Injectivity verification in o(n) space and O(n) time

The problem I want to solve is this: Given a list $A$ of $n$ elements, I want to verify that they are all distinct. If I were to do this "myself", I would need $O(n)$ space and $O(n\log n)$ time to ...
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58 views

Can you determinize an NFA in PSPACE?

QUESTION Given some NFA $A$, can you simulate the determinization of it (using Subset-Construction for example) while remaining in $PSPACE$? MORE DETAILS I'm asking this as I want to be able to ...
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51 views

TQBF PSPACE-COMPLETE : Why this algorithm is exponential but Savitch's not?

So this is a question pertaining to the proof for $PSPACE-COMPLETE$ (for TQBF for example). The idea is to first prove the $L$ $is$ $PSPACE$(easy part) and next is to prove $PSPACE-COMPLETE$. The ...
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79 views

Proving that $NPSPACE\subseteq PSPACE$ using the proof of Savitch's Theorem

We were shown a proof of $NPSPACE\subseteq PSPACE$ in class. In short, the proof says: Let $L\in NPSPACE$. Then there exists a non-deterministic polynomial space bounded Turing machine $M$ that ...
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Logarithmic reduction from Clique to Half-Clique

so the question is in the title basically but I am now studying for a Complexity Theory Exam and encountered this problem in the exercises. I understand how to make a poly-reduction but I am not able ...
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312 views

Worst Case Space Complexity of Merge Sort and Bubble Sort

I understand that the worst space complexity of Bubble Sort is constant O(1), since all the space we need is the array where the elements were stored. But why is Merge Sort's worst space complexity O(...
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Is the language $L = \{(M,m,n)|\exists x \in \{0, 1\}^n:M$ uses $m$ space on input $x$$\}$ decidable?

I have stumbled upon this language: $L = \{(M,m,n)|\exists x \in \{0, 1\}^n:M$ uses $m$ space on input $x$$\}$. At first, it looked like an undecidable problem, but I have failed to prove it, and now ...
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Is PSPACE vs NEXPTIME known?

I know that P = PSPACE is a famous open problem, and that EXPTIME = NEXPTIME is also unknown. By the time heirarchy theorem we know that NP is a strict subset of NEXPTIME. Is anything known about ...
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1answer
271 views

Sorting an array of strings by length in linear complexity

I am trying to find an algorithm to sort an array of strings by length in O(n) time complexity, and O(1) space complexity. The max length of the strings is known. Because of that, I tried using ...
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Why is the run time of an $f(n)$ space decider bounded by $2^{O(f(n))}$?

In the proof of Savitch's theorem from the 3rd edition of Sipser's Intro to Theory of Computation, Sipser claims that the maximum time that an $ f(n) $ space nondeterministic Turing machine that halts ...
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69 views

Algorithm to compute sum of cost of all path between pair of unique vertices of a tree

Given tree is undirected graph. It has n vertices and n-1 edges. The algorithm should compute the sum of cost of all path between pair of unique vertices. Thus, there are total nC2 or n(n-1)/2 such ...
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1answer
27 views

$NL^2 = NDSPACE(\log^2n)$ is closed under complement

From Savitch's theorem we have $NL^2 \subseteq L^4$, which is deterministic and thus closed under complement. From Immerman–Szelepcsényi theorem we have $NL = coNL$. Why then $NL^2 = coNL^2$
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How to prove $L \notin \texttt{DSPACE}(f)$

I want to prove that a language $L$ is not in $\texttt{DSPACE}(f(n))$, the class of languages that a deterministic Turing machine can decide with fixed tape length of $f(n)$ (wiki). That is, I want to ...
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19 views

Complexity and hardness of undirected path

Let $PATH = \{(G,s,t) \mid \exists \text{path from}~s\text{ to }t\text{ in }G\}$, where $G$ is a directed graph. We know that $PATH$ is $NL$ complete. I am wondering what the complexity class of $PATH$...
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Space(n) and Space(n^2) implications

I've a problem where I have to prove the following statements: (i) if $SPACE(n) \subseteq P \implies SPACE(n^2) \subseteq P$ (ii) if $P = SPACE(n) \implies SPACE(n) = SPACE(n^2)$ For the Space ...
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NL-Hardness of Target

When revising for an upcoming exam in complexity theory, I came across this problem on the final part of a question, which I was unable to solve: $ TARGET = \{<G, t> : t\ is\ reachable\ from\ ...
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917 views

Difference between auxiliary space v/s space complexity

I'm confused between these two terms as for example - the Auxiliary space of merge sort, heapsort and insertion sort is $O(1)$ whereas Space complexity of merge sort, insertion sort, heapsort is $O(n)$...
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678 views

Do regular languages belong to Space(1)?

I was wondering, if we take some regular language, will it be in Space(1)? For a regular language X, for instance, we can construct an equivalent NFA that matches strings in the regular language. ...
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32 views

Can CNF with an input string be evaluated in logarithmic space?

I have been trying to solve satisfiability of {$<c, w>$ | $c$ is a CNF and $w$ is a binary string which satifies the $c$}. As first looks to me, it is satisiable in linear time ($O(n)$) since ...
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40 views

Generalized geography game graph

I'm studying the Sipser textbook for my theory of complexity class. In a part of the book (i.e., Space Complexity chapter), for showing that Generalized Geography game is PSPACE-complete, the author ...
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1answer
112 views

Merge sort in place

I don't quite understand why in-place sort merge sort isn't preferred over not-in place? Is it because theoretically in place merge sort is better because of its memory complexity tradeoff, but in ...
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1answer
168 views

How to prove that {<M1, M2> : M1 and M2 are two DFAs and L(M1) $\neq$ L(M2)} is in NL?

My idea is to find a turing machine which recognizes this language in $\log N$ space, could anyone give me some clue on how to find such turing machine?
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Constructing a DFA $M$ such that $L(M) = L(A) \bigtriangleup L(B)$ with a kind of log-space TM

Suppose that $A$ and $B$ are DFAs. We know that there is some DFA $M$ such that $L(M) = L(A) \bigtriangleup L(B)$, the symmetric difference. Also, we can construct this $M$ by some Turing machine $N$. ...
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114 views

How to prove SPACE-TMSAT is PSPACE-hard?

I understand that the language: $\operatorname{SPACE-TMSAT} = \{⟨M, w, 1^n⟩ : \text{DTM $M$ accepts $w$ in space $n$}\}$ is in PSPACE since it doesn't use more than $n$ space. But to prove that it ...
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144 views

Non-existence of PSPACE-hard unary language

I'm trying to prove that unless $\mathsf{P}=\mathsf{PSPACE}$, there is no unary language which is $\mathsf{PSPACE}$-hard. Assuming there is an unary language $A$ which is $\mathsf{PSPACE}$-hard, it ...

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