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Questions about decision problems that can be solved on nondeterministic Turing machines in time polynomial in the length of the input.

3 votes

Sequence to explore the complexity of the NP problem

Could you simulate that in an NP-hardness proof? Or you might start by building an NP-hardness proof from a "nearby problem" that has similar characteristics. …
Juho's user avatar
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2 votes

Relationship between complexity classes W[1] and NP?

But ETH is stronger than P not equal to NP, so its falsification doesn't settle P = NP (but of course, if true, ETH would imply that P is not equal to NP). …
Juho's user avatar
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5 votes
Accepted

Has anyone seen a NP graph problem like this before?

The problem is NP-complete even on planar graphs according to [1], but I don't know about its complexity on partial grids. …
Juho's user avatar
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4 votes

Can someone explain why the MAX-CUT problem is in NP?

The certificate is a coloring of the vertices into red and blue (i.e., a partition into two sets). Given such a certificate, you can iterate through all the edges and count the number of edges whose e …
Juho's user avatar
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4 votes
Accepted

Prove the red blue separation problem is NP-complete

MSP is NP-hard. The hardness was first shown by Eades and Rappaport by a reduction from TSP, see [1], Section 2 for the reduction. [1] Eades, Peter, and David Rappaport. …
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5 votes

Problems that are NP but polynomial on graphs of bounded treewidth

Typically, for many "local problems" such as $\mathsf{Vertex Cover}$ or $\mathsf{IndependentSet}$ (meaning a solution can be verified by checking the neighborhood of each vertex), standard dynamic pro …
Juho's user avatar
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5 votes

Is there any strategy to brute force search?

The answer to both of your questions is yes! Definitely, even though in the worst-case you will have to enumerate the whole search space with brute-force (to prove there is no solution), it absolutely …
Juho's user avatar
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1 vote

Negative simple path NP-Complete

Let $G=(V,E)$ be an instance of Hamiltonian $st$-path. Construct an instance of negative $st$-path $G'$ such that $G' = G$ with a new vertex $t'$ and the edge $tt'$ added. Set the weight of $tt'$ to $ …
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4 votes

Is there any NP-hard problem which was proven to be solved in polynomial time or at least cl...

A polynomial-time algorithm for an NP-hard problem is not known nor expected to exist. … But I think your underlying question is whether or not there are examples of natural NP-hard problems that are, in some sense, easier to solve than some other NP-hard problems. …
Juho's user avatar
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17 votes

What does the 2 in a 2-approximation algorithm mean?

Typically, we use $\alpha < 1$ for maximization problems, and $\alpha > 1$ for minimization problems, where $\alpha$ is the approximation guarantee. So, a $2$-approximation algorithm returns a solutio …
Juho's user avatar
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