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Problem Detail: Integer linear programming (ILP) is an incredibly powerful tool in combinatorial optimization. If we can formulate some problem as an instance of an ILP then solvers are guaranteed to find the global optimum. However, enforcing integral solutions has runtime Read More …

Problem Detail: The decision problem Given a Boolean formula $phi$, does $phi$ have exactly one satisfying assignment? can be seen to be in $Delta_2$, $mathsf{UP}$-hard and $mathsf{coNP}$-hard. Is anything more known about its complexity? Asked By : sdcvvc Answered By : Juho Your Read More …

Problem Detail: One way of looking at regular expressions is as a constructive proof of the following fact: it’s possible to construct the regular languages by starting with a small set of languages and combining them via a small, fixed set Read More …

Problem Detail: Suppose you had a set $P$ of people. Every person $p_j in P$ is familiar with atleast one other person $p_i$ (familiarity is symmetric). Is there a subset $S$ of people such that for $|S| ge k$, no two Read More …

Problem Detail: 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 the $n!=6$ orderings Read More …

Problem Detail: In an assignment I’ve been asked to find a CFG for $a^x b^y a^z b^w$, where, $x,y,z,w in mathbb{N}^+$, $y > x$, $z > w$, and $x+z = y+w$. A hint was given, think of the language as $(a^p Read More …

Problem Detail: A list of n strings, each of length n, is sorted into lexicographic order using the merge-sort algorithm. The worst case running time of this computation is __________. $O(n log n)$ $O(n^2 log n)$ $O(n^2 +log n)$ $O(n^2)$ My Read More …

Problem Detail: In the following two threads I specified the question in the wrong way (easier to solve that way). Proving that finding wheel subgraphs is NP-complete Reducing from Hamiltonian Cycle problem to the Graph Wheel problem My sincere apologies.. I Read More …

Problem Detail: I read on Wikipedia that unification is a process of solving the satisfability problem. At the same time, I know that such solvers are called “SAT solvers” or “SMT solvers”. So, are they different names for the same thing? Read More …