Notes on the Problem Set | Last modified Oct 28 2007

The Regional Chief Judges (Andy Harrington, Ron Pacheco, and Eric Shade) rank the problems as follows, with the author's name in parentheses:

Very Easy
  The Seven Percent Solution (Eric)
Easy
  Rock Skipping (Eric)
Easy/Moderate
  Electronic Document Security (Eric) and Persistent Bits (Andy)
Moderate
  Here We Go(relians) Again and Typesetting (Ron)
Moderate/Hard
  Guard (Andy)
Hard
  Slink (Ron)

Several problems have two solutions provided in the problem directories listed:

gorelian: gorelian.java, gorelian2.java
  Ron first coded the more efficient Dijkstra algorithm in gorelian.java. We wanted to allow teams to use the slower but more quickly coded Floyd/Warshall algorithm in gorelian2.java. Sites are encouraged to compile and run gorelian2.java to make sure it runs in under a minute on your machines.
slink: slink.java, slink2.java
  The original solution is Ron's slink.java, derived from his solution to the more general Slitherlink puzzle. Andy provided a shorter slink2.java as a double check of the Slink problem.
bits: bits.java, bits2.cpp
  The short and quick bits.java uses bit operations. The longer bits2.cpp avoids those operations.

This is an unusual problem set. The only problems that we feel confident in ranking are The Seven Percent Solution, which every team should get, and Slink, which few teams will get. Persistent Bits is in many ways an easier problem than Rock Skipping, but the latter is more straightforward, so it's likely that more teams will attempt it first. Electronic Document Security, Typesetting, and Guard all have short solutions, but it takes some thought to see them, so teams may end up writing much longer solutions than necessary. Gorelians is just Dijkstra's algorithm in a Halloween costume, so teams that see through the disguise may get it quickly. In any case, with eight problems we think that very few teams, if any, will solve them all.

Please help us out and submit a problem!