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Questions related to the (computational) complexity of solving problems
1
vote
How to prove that there is no better algorithm
I presume that $L$ is the length of $D_m$ for all machines.
Hence your input is of size $O(|M|\cdot (L+|A|))$ because it contains $|A|$ activities for all machines and the $D_m$ array of length $L$ fo …
1
vote
How to prove that this problem is NP-complete (or NP-Hard)
You may think that your algo is pseudo-polynomial because the outer loop repeats $T$ times and the possible size of $T$ grows exponentially with a bit string describing $T$. But notice that $R_k(t)$ i …
0
votes
Complexity for optimized k-sum problem
In case we desire that all indices are distinct one can use balanced BSTs such as an AVL-Tree to check if indices overlap. For each of the $O(n^{k/2})$ sums you also store the set of indices (using a …
8
votes
Accepted
Is it possible for the runtime and input size in an algorithm to be inversely related?
Well an algorithm with $O(0)$ fulfills the criterion. It basically does nothing. As soon as your algorithm does at least one operation on execution it has a runtime cost $t(n) > 0$.
Since $$t(n)\in O …
1
vote
Can you say anything interesting about a language knowing only that it is prefix-closed?
If $P$ and $Q$ are languages closed under prefix, then
$P\cup Q$, $P\cap Q$, $P \cdot Q$, $P/Q$ are also closed under prefix. Also you can think of such a language $L$ as a directed tree. Define the g …
1
vote
Accepted
Show that the OR of n variables cannot be expressed as a polynomial over Fp of degree less t...
Let $AND:\{0,1\}^n\mapsto\{0,1\}$ be a polynomial in $GF(q), q\geq 2$.
Notice that the polynomial can't have a constant term (the constant term is zero), because
$AND(0,...,0) = 0$.
Meaning we can wri …
2
votes
Accepted
Are there any NP-complete problems that are also in IP?
$$
IP = PSPACE
$$
According to wikipedia.
Thus $NP \subseteq IP$ and all NP-complete problems are in $IP$.
4
votes
If X is in NP then $\overline{X}$ is in NP. True, false or "we don't know"? Why?
The answer is unknown.
If $X\in NP$ and $\bar X\in \mathcal{NP}$ than by definition it's a so called "co-NP" problem ($X\in \mathcal{coNP}$). It's still an open problem if $\mathcal{NP} = \mathcal{coN …
3
votes
Is maximal independent set on maximal planar graphs still NP-complete?
This is more of a comment, but I want to append an image. The following graph is maximal planar and every node has degree 4, thus the proposed algorithm does not work. The maximal independent set of t …
1
vote
Accepted
algorithm for checking satisfiability
Here is how I would do it:
Algo: Verifier for DNF-SAT problem given as array of closures and a possible mapping of literals to booleans
Input:
Array of closures: [$C_1$,$C_2$,...,$C_m$]
where $C_j \ …
1
vote
Proving complexity of $T(n)=2T(n/3 + 1) + n$ non-Akra-Bazzi
You want to prove a tight $\Theta(n)$ bound as @vonbrand commented you could to show:
$$am+b \leq T(m)\leq cm+d\quad (1)$$
Now start by assuming $(1)$ holds for all $m < n$ and conclude:
$$T(n) = 2T( …
0
votes
How can we show that P is not closed under taking all long prefixes?
Big hint based on Yuvals Hint: Consider the language $\{\langle S, f \rangle | S \text{ is a SAT formula and } f\text{ a satisfying assingment}\} \in P$