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Alex Bowe

stuff I'm thinking about

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DRY Function Pointers in C

September 9, 2013 by Alex 4 Comments

Just a quick post today about C function pointers. Over the past two years I have seen the occasional function pointer introduction post on Hacker News, but I rarely see this one weird trick. The most recent I have read was this one by Dennis Kubes. I haven’t hung out with C for a while […]

Succinct de Bruijn Graphs

July 2, 2013 by Alex 17 Comments

This post will give a brief explanation of a Succinct implementation for storing de Bruijn graphs, which is recent (and continuing) work I have been doing with Sadakane. Using our new structure, we have squeezed a graph for a human genome (which took around 300 GB of memory if using previous representations) down into 2.5 […]

Failing at Google Interviews

September 24, 2011 by Alex 57 Comments

I’ve participated in about four sets of Google interviews (of about 3 interviews each) for various positions. I’m still not a Googler though, which I guess indicates that I’m not the best person to give this advice. However, I think it’s about time I put in my 0.002372757892 bitcoins. I recently did exactly this to […]

FM-Indexes and Backwards Search

August 24, 2011 by Alex 8 Comments

Last time (way back in June! I have got to start blogging consistently again) I discussed a gorgeous data structure called the Wavelet Tree. When a Wavelet Tree is stored using RRR sequences, it can answer rank and select operations in $\mathcal{O}(\log{A})$ time, where A is the size of the alphabet. If the size of […]

Wavelet Trees – an Introduction

June 28, 2011 by Alex 8 Comments

Today I will talk about an elegant way of answering rank queries on sequences over larger alphabets – a structure called the Wavelet Tree. In my last post I introduced a data structure called RRR, which is used to quickly answer rank queries on binary sequences, and provide implicit compression. A Wavelet Tree organises a […]

RRR – A Succinct Rank/Select Index for Bit Vectors

June 1, 2011 by Alex 4 Comments

This blog post will give an overview of a static bitsequence data structure known as RRR, which answers arbitrary length rank queries in $\mathcal{O}(1)$ time, and provides implicit compression. As my blog is informal, I give an introduction to this structure from a birds eye view. If you want, read my thesis for a version […]

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Recent Posts

  • DRY Function Pointers in C
  • Succinct de Bruijn Graphs
  • Failing at Google Interviews
  • FM-Indexes and Backwards Search
  • Wavelet Trees – an Introduction
  • RRR – A Succinct Rank/Select Index for Bit Vectors
  • Generating Binary Permutations in Popcount Order
  • Some Lazy Fun with Streams
  • Design Pattern Flash Cards
  • Metaprogramming Erlang the Easy Way

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