# Questions tagged [polynomial-time-reductions]

Used in questions asking for efficient (polynomial-time) reductions between computational problems.

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### If A ∈ coNP, B ∈ NP and $NP \neq coNP$, is it possible to Karp reduce A to B?

If A $\geq_p$B and $B\in NP$, $A\in coNP$, then we can build a Turing machine $M_A$ using $M_B$ machine of B. Input: w We make a new word with a reduction function $f(w)$. Then we run $M_B$ on $f(w)$ ...
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### Reducing the Independent Set Problem to Independent Set for 3-Colorable Graphs

I am exploring a reduction from the general Independent Set Problem to the Independent Set Problem specifically for 3-colorable graphs. The goal is to demonstrate that the maximal independent set of a ...
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### K-Assignment Search to Decision

Given a set of variables X, and a set of subsets of these variables, each set of size k (each subset includes exactly k variables), we would like to find an assignment 1...k to each variable such that ...
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### Showing the language of all graphs that are both 4-colorable and not 3-colorable is coNP-hard

As the title states, I need to prove that the language of all graphs that are both 4-colorable and not 3-colorable is coNP-hard. I'm not looking for a solution but a clue or something to help me ...
1 vote
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### NP, NP-Hard and NP-Complete

If a problem S is NP-Complete and we know that a problem Q is polynomial time reducible to S. Does that mean that Q belongs to NP? Also, when can we state that Q is NP-Hard but does not belong to NP? ...
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### Cardinalities in set coverings

Let $I$ be a set of items; $C \subseteq \mathcal{P}(I)$ be a set of subsets of $I$, where $\mathcal{P}(I)$ stands for the power set of $I$; And $C(i) = \{ c \in C \mid i \in c \}$ be the set of sets, ...
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### Why does this approach not work on the SubSet Sum Problem?

I was reading this post, and in it I learned how to make difficult instances of the SubSet Sum Problem. There the guy who responded to the post says that it is necessary to have density 1.0 and all ...
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### Is it possible to find reductions from problems in $\mathsf{NP}$ to SAT based solely on the certificate verification algorithm?

The following problem has made me ask this question: Given a boolean formula $\varphi(X)$ decide if there exists a quantification of $\varphi(X)$ with $k$ $\forall$ quantifiers that holds true. ...
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### Problem about $NP \neq coNP$

I need to show that assuming $NP \neq coNP$ then there are 2 non-trivial languages $A$ and $B$ ($A,B \neq \emptyset, \Sigma^*$) in $NP \cup coNP$ such that there's no polynomial time reduction from A ...
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### Reduction from dominating set to disconnected dominating set

Consider an undirected graph $G = \langle V, E\rangle$, and a set $S\subseteq V$ of vertices. We say that $S$ is a dominating set, if for every vertex $v\in V$, it holds that $v\in S$, or $v$ has a ...
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### How to construct complement of NFA universality?

Given an input NFA, can one construct an NFA that is universal (that is, accepts all its inputs) if and only if, the input NFA isn't universal? I tried to use the fact that NFA-universality is PSPACE-...
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### Reduction from Hamiltonian path to Tripartite decision problem

I teach a fairly advanced algorithms class to high schoolers and I accidentally presented them with a bunk reduction from Hamiltonian path to the Tripartite graph decision problem. My attempt involved ...
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### HAMILTONIAN PATH AND SUBSETSUM

If we were to discover a deterministic algorithm capable of deciding, in polynomial time, whether a given graph contains a Hamiltonian path, would that imply that the problem SUBSETSUM belongs to P? ...
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### Choose elements from sets that form a permutation: NP hard?

Let $n$ be a positive integer and $[n] := \{1,2,3,...,n\}$. You are given $k$ non-empty subsets of $[n]$. Decide whether it is possible to select exactly one element from each subset such that the ...
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### Reduction from novel problem to Set Cover

i would like to perform a reduction for my novel problem to preferably the set cover problem, but i am a bit lost.. My problem can be described as follows: Suppose you have given an binary word as ...
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### Is finding a Polytime reduction from $L_1$ to $L_2$ equivalent to proving $L_2 \in P \Rightarrow L_1 \in P$

I often hear NP-completeness as problems such that, if they were in $P$ all problems in $NP$ are in $P$. The true definition, though, is that NP-complete is a set of languages in NP that all languages ...
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### Reduction between problems where problem A solves problem B with probability $\frac{2}{3}$

Suppose we have a problem, $A$, and a machine $T_A$ that solves $A$. Now, let's say we have a problem $B$ that is solvable with a polynomial number of calls to $T_A$, and we call $T_B$ the machine ...
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### Does there exist an FPTAS for bin packing problem?

We know that there does not exist an FPTAS for the bin packing problem because it is a strongly NP-HARD problem, as the 3-partitioning problem which is strongly np-hard, can be reduced to the bin ...
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### Partition a family of sets to maximize cumulative overlap and cardinality

My problem is this: I have a list of $n$ items $N$ (think of them as the natural numbers $1,\dots,n$) and $m$ subsets of $N$ $S_1,\dots,S_m$ which may overlap. The objective is to find a partition of ...
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### Show problem is NP-hard

I'm preparing for my exam and I got stuck on the following problem: The gardening problem: We have access to a set of different types of seeds and a number of plant pots.For each plant pot, there is ...
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### Choosing the ideal problem to prove the hardness

I am research scholar currently working in complexity theory. Recently, i have started working on hard proofs and reductions. It is very well established that there is a polynomial reduction from ...
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Let $A$ be any unary language. Prove that if $A$ is NP-complete, then P=NP. Approach 1: We just have to prove that we can decide $A$ in polynomial time. Consider a Turing machine that on input $w$, ...
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### I would not be able to get my simulation in my life time

I am running a simulation on my computer. I tried to multiply two polynomials $g(x), h(x)\in GF(2)[x]$, with $degree(g(x))= 8165$, and $degree(h(x))=25$. This multiplication took almost $20$ minutes ...
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### Given the optimal coloring of a graph how will we find the optimal coloring of its complement graph?

Suppose the optimal color assignment of graph $G$ is given. Does there exist any polynomial-time algorithm that provides the optimal color assignment of its complement graph $\overline{G}$? A ...
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### If you can reduce A to B, does that mean B reduces to A?

If you can reduce A to B, does that mean B reduces to A? Sorry for the stupid question. I think the answer should be yes, because if you can convert all yes-instances of A to yes-instances of B, then ...
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### Prove minimum vertex bisection problem is reducible from bisection width, thereby proving NP-Completeness

The bisection width problem gives you a yes or a no -> if there exists a bisection of size at most $K$ for $G=V,E$. Minimum Vertex Bisection problem gives you a bisection of the smallest size. ...
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### Reduction from vertex-cover to system of quadratic equations

Define $$\text{SQE}=\{S\ |\ S\ \text{is a system of quadratic equations with real solutions}\}$$ and $$\text{VC}=\{G\ |\ G\ \text{is a simple undirected graph with a vertex cover}\ \leq k\}$$ I am ...
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### computation P=L [duplicate]

i have the following question which I'm having some hard time to solve: prove: if every two Languages $A$ and $B$ that have a polynomial reduction ($A$ to $B$) also have a log space reduction ($A$ to ...
1 vote
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### example of an NL-completeness reduction?

I'm looking for simple examples of nondeterministic log-space completeness reductions. In particular I seem unable to construct any nontrivial widget using 2-SAT clauses, which is known to be NL-...
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