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Questions regarding well-defined instructions for completing a task, and relevant analysis in terms of time/memory/etc.
3
votes
Accepted
Choosing 2*n values while evaluating Fast Fourier Transform
Symbolic multiplication of degree $<n$ polynomials $A(x)$ and $B(x)$ would take $O(n^2)$ time. That may be fine, but they are giving an algorithm that takes $O(n \log n)$ time, which is better.
Inste …
14
votes
Generalizing the "median trick" to higher dimensions?
This is a neat question and I've thought about it before. Here's what we came up with:
You run your algorithm $n$ times to get outputs $x_1, \cdots, x_n \in \mathbb{R}^d$ and you know what with high …
2
votes
Algorithm for finding heavy hitters in a weighted stream
Here's a generic randomized solution. (Do we even have deterministic solutions in the unweighted case? Don't Space Saving and Batch Decrement both need hash maps?)
This is probably not the ideal solut …
17
votes
Accepted
Matrix permanent is 0
Expanding my comment:
Computing the permanent of a matrix is #P-hard (Valiant 1979) even if the matrix entries are all either 0 or 1.
We can interpret a matrix $M \in \{0,1\}^{n \times n}$ as a bipa …
6
votes
Accepted
Min Hamming distance of a given string from substrings of another string
Elaborating Paul's suggestion for a $O(n \log n)$-time algorithm:
Input: Let $u \in [m]^k$ and $v \in [m]^n$ with $k \leq n$, where $U=[m]=\{1,2,\cdots,m\}$.
Define polynomials $$p(x,y) = \sum_{i \i …
16
votes
Complexity of Finding the Eigendecomposition of a Matrix
Finding eigenvalues is inherently an iterative process: Finding eigenvalues is equivalent to finding the roots of a polynomial. Moreover, the Abel–Ruffini theorem states that, in general, you cannot e …