# Questions tagged [polynomial-time]

Use for algorithms, algorithm-analysis and complexity-theory questions that aim for polynomial running time resp. time complexity. Such questions often are are reference-requests or about runtime-analysis or time-complexity.

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### Propositional formula in DNF can be decided in polynomial time?

For a given propositional formula f in DNF, one can decide in polynomial time, if the formula is satisfiable: Just walk through all subformulas (l_1 and ... and l_k) and check, wheter it has NO ...
2answers
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### Can the isomorphic graph problem be solved in deterministic polynomial time?

Here is a recent homework problem of mine: Call graphs G and H isomorphic if the nodes of G may be reordered so that it is identical to H. Let ISO = {⟨G,H⟩| G and H are isomorphic graphs}. Show ...
2answers
747 views

### Why is it important to solve a problem in Polynomial time, In cryptography?

I have just started to learn Cryptography. I am trying to learn "Merkle-Hellman Knapsack Cryptosystem". So, right at the beginning of the discussion, a question came in my mind: Why is it important ...
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177 views

### Unary in $P$, binary not in $P$

I would like to know if there is a known decision problem with the following characteristics: Represented in unary, the problem is decidable in polynomial time. Represented in binary, the problem is ...
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2k views

### Does two languages being in P imply reduction to each other?

Given two languages $L_1$ and $L_2$ that are in $\mathsf{P}$, can it be proven that there is a polynomial time reduction from $L_1$ to $L_2$ and vice versa? If so, how? I noticed that if $L_1$ is the ...
1answer
117 views

### Is every language in PTime also context-sensitive?

Context-sensitive languages are exactly those that can be recognised using linearly bounded automata, i.e., those in NSPACE(O($n$)). This subsumes all languages that can be recognised in linear time, ...
1answer
218 views

### A Reduction from XORSAT to 2-SAT

Does anyone know of a non-trivial reduction from XORSAT to 2-sat since they are both in P? (By non-trivial I mean one that does not just solve the instance of XORSAT and map it to a fixed instance of ...
2answers
93 views

### Resource bounded reductions for RE-Complete problems

Given that the halting problem is RE-Complete, we can reduce any problem in RE to an instance of the halting problem. Are there are any results on the time-bounds for this reduction? Can we do this ...
2answers
91 views

### On certificates in BPP (avoiding majority vote)

Assume that we have a $BPP$ algorithm $A$ for a problem $\Pi$. Given input $x$ we run $A$ on $\Pi$ polynomially many times and take majority output. However if the problem $\Pi$ is also in $NP$ ...
1answer
43 views

### Probability of randomly designated subsets cover the universe

Let $U=\{1,2,\ldots,n\}$ and $S \subseteq \mathscr{P}(U)$. Let $T$ be a subset of $S$, randomly constructed selecting independently each element of $S$ with probability $p$. Is there a polynomial ...
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375 views

### Linear programming restricted to rational coefficients

I'm reading the appendix A of Williamson's "the design of approximation algorithms" about linear programming. In the definition of a linear programming it restricted the coefficients of cost function ...
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72 views

### Machine with an oracle for a language that cannot decide another language in polynomial time

We usually see examples of languages contained in $P^A$ for some language $A$, or cases where $P^A=P^B$ (or $P^A\subseteq P^B$) for two languages $P^A$ and $P^B$. However, there is any explicit ...
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### Complexity of the decision version of determining a min-cut

I was wondering what the complexity of the following problem is: Given: A flow network $N$ with a source $s$, sink $t$ and a number $k$. Question: Is there an $s$-$t$ cut of capacity at most $k$? ...
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### Subset Sum Search Problem for Input with At Most One Solution [closed]

Edit: This question has been reasked on TCS. We first consider the search version of the subset sum problem: Given a set $S$ of $n$ naturals, find a subset of $S$ that sums to exactly $W$. My ...
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### Polynomial time algorithms on strings [closed]

I am looking for familiar problems on strings of finite length over an finite alphabet, where a polynomial time algorithm is known. To be more precise, let $\Sigma$ be a finite alphabet. I am looking ...
2answers
811 views

### Solve parity game in polynomial time?

Is it possible to solve a parity game in polynomial time? If yes, how? If no, why not?
2answers
113 views

### For some $n$, how can we check whether there exists $a,b \in \mathbb{N}$ such that $a^b = n$ in polynomial time?

For some given $n$, how can we check whether there exists $a,b \in \mathbb{N}$ ($b > 0$) such that $a^b = n$ in polynomial time with respect to the number of digits in $n$?
3answers
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### Can't understand why the DP Subset Sum algorithm is not polynomial

I can not understand why the dynamic programming algorithm for the Subset Sum, is not polynomial. Even though the sum to find 'T' is greater than the total sum of the 'n' elements of the set , the ...
2answers
940 views

### Polynomial-time algorithm with exponential space is eligible?

I'm curious about two things. When we define the class called "probabilistic polynomial-time algorithm" in computer science, does it include polynomial-time algorithm with exponential space? For ...
2answers
913 views

### If A is poly-time reducible to B, is B poly-time reducible to A?

Basically, is the following statement true? $A \leq_p B$ $\rightarrow$ $B \leq_p A$
1answer
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### Finding number not in list with wildcards

I have a list like this: 1*0*0 1**0* 0*0** 001** Where the number of elements in each row is $n$ and * is a wildcard for 0 or 1. I need a polynomial-time ...
1answer
273 views

### Time complexity of languages that are polynomial time reducible to NP complete languages

I am wondering if given the time complexity of an NP-Complete problem or at least some information about it for example if $SAT\in Time(2^{sqrt(n)})$ (hypothetically) could I assume that all ...
2answers
887 views

### What is a Turing Machine in class coNP

On the wikipedia article about the polynomial hierarchy http://en.wikipedia.org/wiki/Polynomial_hierarchy it says "$A^B$ is the set of decision problems solvable by a Turing machine in class A ...
1answer
173 views

### Minimum diameter spanning tree problem

Minimum diameter spanning tree (MDST) problem is defined as following: given the connected weighted graph $G(V, E)$, weight function $w: E \rightarrow R, w(e) > 0\ \forall e \in E$, find the ...
2answers
929 views

### Is it true that P is not equal to deterministic linear space complexity class?

I'm curious, how could I know that P (polynomial time complexity class) is not equal to deterministic linear space complexity class? Is there some proof? Or should I find some algorithm which is not ...
1answer
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### How do we show that the polynomial time reduction of one problem to another has been done in polynomial time?

I have just been reading through a SO post which proves that the Halting Problem is NP-Hard. Whilst this is an easily followed proof, one slight slight aspect of it has left me scratching my head: it ...
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407 views

### Computationally 'hard' polynomial-time reduction to other NP-complete problems / Hierarchy of NP-complete problems

As we all know there exist plenty of polynomial-time reductions from one NP-complete problem to another. Are there any NP-complete problems that have a rather large polynomial bound for reductions to ...
2answers
174 views

### GOTO vs. including line in loop - will it affect efficiency?

Let's say I have an algorithm something like as follows: ...
1answer
67 views

### Do poly-time algorithms exist whose time complexity is unprovable?

If not, is there a decision procedure that successfully classifies any polynomial time algorithm as poly-time within a time polynomially bounded by the length of the input algorithm?
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### Can we use reductions to design approximation algorithms for NP-hard problems?

Let us say that I have a problem $P(n)$ that I need to solve (where $n$ is the size of the input of problem $P$). I used a polynomial-time reduction from a known NP-hard problem $Q(m)$ (where $m$ is ...
2answers
358 views

### Why does a polynomial-time language have a polynomial-sized circuit?

I wish to understand why P is a subset of PSCPACE, that is why a polynomial-time langauge does have a polynomial-sized circuit. I read many proofs like this one here on page 2-3, but all the proofs ...
1answer
326 views

### Polynomially related lengths under two different encodings

I'm reading through "Computers and Intractability: A guide to the Theory of NP-Completeness" by Michael R. Garey and David S. Johnson, p. 20 and I came across this ...
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### $m/p$-equivalence holds after union with an arbitrary finite language

Problem 1: Let $A,B$ be languages over some alphabet $\Sigma$, if $A \equiv_m B$, then for every finite language $C$, $A \cup C \equiv_m B \cup C$. Problem 2: Problem 1 but using polynomial time ...
1answer
148 views

### Methods of turning a decision problem into finding the certificate?

I usually find this in the context of asking about NP-complete problems, but any decision problem works. We start by assuming there's a polynomial time algorithm that gives the yes or no answer. If it'...
1answer
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### Characterizing the range of a polytime function

Is it true that an infinite language is in P iff it is the range of a length increasing polytime function? I ask because I know that it is a basic result in computability theory that a set is ...
1answer
179 views