Computer Science Weekly Newsletter

Computer Science newsletter

Top new questions this week:

Are "Flow Free" puzzles NP-hard?

A "Flow Free" puzzle consists of a positive integer $n$ and a set of (unordered) pairs of distinct vertices in the $\:n\times n\:$ grid graph such that each vertex is in at most one pair. $\:$ A ...

np-hard square-grid  
asked by Ricky Demer 8 votes
answered by Hendrik Jan 0 votes

Solving recurrence relation with two recursive calls

I'm studying the worst case runtime of quicksort under the condition that it will never do a very unbalanced partition for varying definitions of very. In order to do this I ask myself the question ...

algorithm-analysis runtime-analysis recurrence-relation  
asked by nightcracker 8 votes
answered by Yuval Filmus 7 votes

What exactly is an algorithm?

I know that this may sound a bit out of the box, in fact i used to always think inside the box, but recently i've been thinking, possibly because computer science provides an high degree of freedom, ...

algorithms  
asked by Devian Dover 6 votes
answered by ranby 6 votes

Detecting palindromes in binary numbers using a finite state machine

In my first algorithms class we're creating these patterns that are supposed to model a finite state machine. We were given a task to think if we can figure out a way to detect palindromes in binary ...

regular-languages finite-automata  
asked by Jakub Arnold 5 votes
answered by babou 4 votes

Determining Number of States in a Turing Machine

I am looking at an example Turing machine in my textbook, Automata and Computability by Dexter C. Kozen, and I'm confused as to how they determine the number of states this particular machine has. ...

turing-machines notation  
asked by tdark 4 votes
answered by babou 3 votes

What problem cannot be solved by a short program?

BACKGROUND: Recently I tried to solve a certain difficult problem that gets as input an array of $n$ numbers. For $n=3$, the only solution I could find was to have a different treatment for each of ...

complexity-theory programming-languages kolmogorov-complexity  
asked by Erel Segal Halevi 4 votes
answered by rosebud 4 votes

Does a graph always have a minimum spanning tree that is binary?

I have a graph and I need to find a minimum spanning tree to a given graph. What is to be done so that the output obtained is a binary tree?

graph-theory binary-trees spanning-trees  
asked by Aditya.M 4 votes
answered by Juho 7 votes

Greatest hits from previous weeks:

Understanding Peterson’s and Dekker’s algorithms

I am trying to understand the algorithms by Peterson and Dekker which are very similar and display a lot of symmetries. I tried to formulate the algorithms in informal language like follows: ...

concurrency synchronization mutual-exclusion  
asked by gbag 13 votes
answered by Wandering Logic 11 votes

How to verify number with Bob without Eve knowing?

You need to check that your friend, Bob, has your correct phone number, but you cannot ask him directly. You must write the question on a card which and give it to Eve who will take the card to Bob ...

algorithms cryptography  
asked by Joe 31 votes
answered by Thomas Pornin 14 votes

Can you answer these?

Finding maximum information gain subinterval of an array containing points from 2 classes

Suppose we have an $N \times 2$ array $A$ where the two entries $A(k,1)$ and $A(k,2)$ give the number of occurrences of each of two classes at position $k$. Given a sub-interval $I$ of indices between ...

algorithms dynamic-programming  
asked by user2566092 2 votes

Check whether a directed, rooted spanning tree is actually some shortest-paths tree in $O(V + E)$ time

Given a directed graph $G = (V, E)$, with all edge weights being non-negative, someone has written a program that he/she claims implements Dijkstra's algorithm. For a fixed starting vertex $s$, the ...

algorithms complexity-theory graph-theory shortest-path graph-algorithms  
asked by hengxin 1 vote

State of art quadratic knacksack algorithms

What is the current status to quadratic knacksack problem? Say, how many variables can the state of art solver handle? Thank you.

optimization combinatorics  
asked by user40780 1 vote
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