Redcode » Algorithms

Orchard Planting: Greatest Common Divisor

royvanrijn — Fri, 30 Dec 2011 12:21:59 +0000

The Orchard Planting contest from infinite search space is over. So it is time for a quick write-up.

The rules are simple, on a grid of integers, place N points on the grid to get as much 4 points on a line and never more then 4 points on a line.

My big break-through [...]

Bytebeat: Algorithmic Symphonies

royvanrijn — Wed, 07 Dec 2011 15:42:08 +0000

A couple of days ago I first encountered “bytebeat”. This is a new hype revolving algorithmic music and sounds. The basic idea is this:

main(t) { for(t=0;;t++) putchar( t * (((t>>12) | (t>>8) ) & ( 63 & (t>>4)))); }

This simple loop has one variable, t (time). And every iteration we use t to [...]

Programming Contest: Orchard Planting

royvanrijn — Mon, 17 Oct 2011 12:07:06 +0000

Yes! Another new programming contest: Orchard Planting

The problem:

On a grid you have to place trees (dots). If there are four trees in a line, you’ll get a point. But: more then 4 trees in a line is illegal. What are the best solutions for N=11 to 60 trees?

Up to now [...]

Meet me at Devoxx 2011

royvanrijn — Fri, 05 Aug 2011 14:53:21 +0000

This year I’ll be presenting at Devoxx in Antwerp, Belgium. In my opinion it currently is the best Java conference in the world. It’ll be my first talk in English.

The titel of the talk is: What Shazam doesn’t want you to know.

During the talk I’ll be explaining how Shazam works and [...]

God’s Dice

royvanrijn — Mon, 09 May 2011 08:07:36 +0000

Yay! There is a new Virtual Source Programming Contest: “God’s Dice”

After a bit of a messy start of the contest, within hours three people had a 100% score (almost, 99.99% due to some rounding errors). This sparked James, the organizer, to change the rules a bit. Now the contest is [...]

Reading iPhone GPS data from backup (with Java)

royvanrijn — Thu, 21 Apr 2011 00:06:24 +0000

Today I noticed the following post on Slashdot: Apple Logging Locations of All iPhone Users

And the article they are referring to can be found here

First I was amazed, how can Apple do this? But on second thought, they aren’t sending it yet to anybody, it is just something on the phone [...]

De Bruijn sequence in constant amortized time

royvanrijn — Thu, 24 Feb 2011 21:29:29 +0000

Follow up on the previous blogpost.

Yesterday I wrote an algorithm in Java to generate de Bruijn sequences. But I had a breakthrough after reading:

K. Cattell, F. Ruskey, J. Sawada, M. Serra, C.R. Miers, Fast algorithms to generate necklaces, unlabeled necklaces, and irreducible polynomials over GF(2)

It has an algorithm which generates Lyndon words [...]

Generating de Bruijn sequences and Lyndon words

royvanrijn — Thu, 24 Feb 2011 09:32:52 +0000

Not so long ago I encountered something called the de Bruijn sequence. For now I’ll only use this for an alphabet of (0,1), binary. But everything said here could also be applied to other alphabets. In this post I’ll describe what this sequence is, and how you can generate them, using Lyndon words.

[...]

Testing a chess engine

royvanrijn — Mon, 07 Feb 2011 09:02:46 +0000

About a week ago I decided to try and write a chess engine. I’ve encountered bitboards before, and I really liked working with them. Most references I found had to do with chess engines, so I decided to have a go.

The single most important and time consuming aspect of building a [...]

Rainbow tables, reverse hash lookup

royvanrijn — Sat, 01 Jan 2011 16:17:25 +0000

Today I’ve been looking into rainbow tables. These are tables used to do a reverse lookup for a hash function. For example MD5, or Windows LAN Manager. Usually these tables are used to find passwords if the hash is known. Now I’m not looking for a method to crack somebodies computer, but the technology and [...]