I used to train hard for the topcoder competition. It's a nice community; and those tutorials are very useful.

The ones that I found more interesting were the ones on line sweep and geometric algorithms.

On Fenwick's Trees; this tutorial http://www.topcoder.com/tc?module=Static&d1=tutorials... is really good. Although, the original paper is well-explained: (link to the author's website) http://www.cs.auckland.ac.nz/~peter-f/ ("A new data structure for cumulative frequency tables")

And on bit manipulation; I highly recommend you read this... you'll be thinking in zeroes and ones for a while... http://www.topcoder.com/tc?module=Static&d1=tutorials...