Sunday, August 28, 2005

Deadly Rooms of Death

Title: Deadly Rooms of Death
Author: Caravel Games
License: Freeware (Architects Edition), Commercial (Journey to Rooted Hold)

The premise of DROD is simple enough: kill all of monsters in each room of each level in the hold (the stronghold, castle type of hold). Your weapon is your trusty sword and your brains. DROD is a turn based puzzle game. You play the indomitable Beethro Budkin. Each turn, you can move one square in any of eight directions or swing your sword 45 degrees. If your sword happens upon a monster, dead it dies. After your move, each of the monsters gets to move. If one of them gets to you, you die.

The key to game is learning the movement rules for each of various monsters. The simple roaches just come straight at you. The smarter goblins will try to attack you from behind. Each of their movement rules are deterministic, and you will need to understand them. If you allow the monsters to surround you, death will soon come. You do have some additional tools. My favorite is the mimic. Mimics are copies of Beethro and move in unison with you. They can help out in places you do not want to venture yourself.

Rooms contain walls to help you trap and isolate the monsters. Divide and conquer is usually the course to take. There are often doors and switches which open, close, or toggle these doors. You have to figure out the correct order to tap the switches to gain access to all of the monsters.

There are two versions of the game. The freeware Architects Edition was released in 2003. The commercial Journey to Rooted Hold was released earlier this year. DROD:JtRH has better graphics and adds several new monster types. Another addition is your nephew Halph. He follows you around and is useful at opening doors and getting in the way of the monsters. For some reason, they do not kill him. The JtRH version also contains a story which plays out as you complete the rooms and levels. The voice acting is a little corny at times, but adds a nice element to the game.

Both versions of DROD are massive in size. Each contains 25 levels. Each level contains 10 to 20 rooms to tame. The room design, variety, and pacing are very good. Some rooms are quite difficult, but I enjoyed the challenge. These are truly wonderful games. I hope everyone tries them. DROD:JtRH will probably be the best logic/puzzle game released this year.

There is a very active DROD community at When DROD:AE was released, a level editor was included. Slightly over one hundred holds designed by various "architects" are available here. These holds are rated in both difficulty and quality. This makes finding holds which are more to your liking much easier. I wish more games had similar two axis rating systems for user made level sets. This site also contains a very intricate help system. It is ok to peek.

There is a 3D version of DROD:AE produced by TLK Games. I played the demo and was not impressed. The game plays better from a top down view 2D perspective.

Here is a review of DROD by another mathematician. In his review, he mentioned the possibility that the DROD is in fact NP-complete. Some time ago, minesweeper was shown to be NP-complete. I decided to give this a think. It did not take long to realize that any 3-SAT problem could be encoded as a DROD room. Here is an example.

The four switches correspond to the variables, and the connected 3-sets of doors correspond to the clauses. To order the gain access to the one roach and complete the room, you need to figure out which switches to tap and simultaneously open at least one door in each of the 3-sets. This amounts to solving a 3-SAT problem.

Thursday, August 18, 2005


Title: JellyFish Light
Author: JellyFish AS
License: Freeware

Title: GNU Backgammon
Author: GNU Backgammon Team
License: GNU General Public License

I realize that backgammon is not a puzzle or logic game, but I am also a fan of two-person strategy games. So, I am going to mix in reviews of computer programs which play such games from time to time. I hope you do not mind.

Over the last 15 years, high-level backgammon has undergone a revolution due to computer backgammon programs. First, there is a fundamental difference between backgammon programs and those that play other games. Due to the additional branching from the various dice rolls, backgammon programs can only look a few moves (or ply) ahead and then have to use very sophisticated heuristics to evaluate the positions. Chess, checker, and othello programs, on the other hand, perform very deep searches, but use relatively simplistic evaluation heuristics. In a backgammon program, it is more important to have a strong evaluation heuristic.

About 15 years ago, backgammon programs started using neural nets to learn good heuristics. Instead of having the programmer code in what are good things and what are bad things in a backgammon position, the programs learn by playing. One of the first program to do this was called TD-Gammon. It played on-line at a backgammon server. I remember playing against it. At first, it was a bit of a joke. Its cube play was atrocious. Over time, it got better, a lot better. Eventually, it was one of the top rated players, if not the top rated player, on the backgammon server. Players and programmers took notice.

Between then and now, several other similar backgammon programs have been developed. These programs have become very good, besting the best human players. But, the humans have fought back. The really interesting aspect in the development of these programs is that human players started looking at the heuristics and learning from them. For example, there are books by Robertie and Bagai which distill information from the heuristics and pass it on to human players. This examination has changed the way high-level backgammon is played.

I want to mention two freeware backgammon programs which use neural net based heuristics. Both play a very strong game. The first is called JellyFish Light. Supposedly, it is called JellyFish because, its neural nets contain as many connections as the brain of a jelly fish. It might be true. In any case, on its highest level, JellyFish beats me far more often than I beat it. I am an average Flight A player, but not an expert level player. The interface is simple but nearly flawless. Jellyfish Light does not contain many bells and whistles. They sell a commercial version with many additional features. However, I find it amazing that they give the Light version away for free.

The second program is GNU Backgammon. It is also a very strong program, but the interface, menus, and documentation are at times a little clunky. GNU Backgammon also beats me up pretty good. It contains many features. My favorite is tutor mode. With this feature enabled, when you make a bad play (how bad is adjustable), it warns you and allows you to look at a chart of its evaluation of the possible moves. This has significantly improved my game. It also has rollout and analysis features. All and all, a very impressive program.

So which one plays a better game? In an extended match, GNU Backgammon beat JellyFish by .12 points/game over 5000 games. This is a statistically significant result. Still, JellyFish is no slouch, and I find myself playing it more often because of its simple but efficient interface. I save GNU Backgammon for when I want a tutoring session.

There are many more strong backgammon programs available, but these two should suffice for almost everyone. A third program which I should mention is Snowie. It is commercial program and quite expensive. I have never played it, but it is currently considered the best backgammon program out there.

For those interested, here is a nice brief overview of the *MinMax algorithm used in backgammon programs. You may want to compare that with MinMax algorithm used in chess programs. My opinion is that the real strength of these backgammon programs comes from their ability to weigh risks and rewards. A key part of the *MinMax algorithm is averaging over the possible dice rolls, both the good and the bad. The computer does this computation without emotion. Human beings are not very good at weighing risks and rewards. It is not part of our nature. I think this is way these programs fair so well against humans.

Friday, August 12, 2005

Laser Tank

Title: Laser Tank
Author: Jim Kindley
License: Freeware
Web Site:

A few weeks ago, a update to the freeware classic Laser Tank was released. Just in case there are two or three puzzle game fans out there who have not heard of this one, I thought I would review Laser Tank this week. The most amazing thing about Laser Tank is its huge online following. People just love it. Users have made over 13,000 levels. And there is an active Yahoo group for Laser Tank. I wish more games had this kind of following.

The goal in each level is simple enough: guide your tank to a flag. Standing in your way are walls, water, and anti-tank turrets. But you have a nifty laser cannon on your tank. It can destroy some types of walls, push special bridge building blocks around, and bounce off mirrors to destroy those pesky anti-tank turrets. The game is played on a 16 by 16 grid and is turn based. You may take as long as you would like to work through a level.

The default download of Laser Tank contains 2030 levels. If you join the Laser Tank Yahoo Group, you can download something like 13,139 more levels. As you can imagine, the quality of the levels varies greatly. There is a system for users to rate levels based on difficulty: Kids, Easy, Medium, Hard, and Deadly. These ratings are quite accurate, but I wish there was a way for users to rate the quality of the levels as well.

Some of the levels are quite difficult. I would say some levels are in fact unfairly difficult. It is possible to make a level in which you have to look 20 moves ahead in order to solve it. It feels like you are performing a depth-first search. Some user made levels seem to be designed this way. There were more than a few levels I just did not enjoy solving. To further justify my point, there are 257 levels which currently "unsolved".

I am sure that the hard core Laser Tankers are calling me a wimp right now. So be it. For those hard core, there is a global high score. If you find a solution which uses fewer moves and shots than the previous best, then you can submit your solution, and your name will appear on the global high score list in the next month's release.

One of my favorite things about the game is the graphics. Looking that screen shot, you might think I am crazy. But, the point is that graphics are simple and functional, but do not get in the way. Puzzle games should be about the puzzles, not about flash. Laser Tank follows this motto. Also, fans have designed over three dozen graphics sets in case you do not like the default. I like the simple "EyeSaver+Grid" graphics, but to each their own.

Laser Tank is a good game, but not a great game. After downloading the latest version a few weeks ago, I played it a fair bit for a week. I had not played it in over a year and had a grand old time. I knocked off another 75 levels bringing my total to around 400. However, by the end of this session, the levels started seeming the same. There is less variety in the levels than one would hope. But, in a year, when the next update comes out, I will probably download it and have another grand old time.

Friday, August 05, 2005

Touch Puf

Title: Touch Puf
Author: Ammar Muqaddas
License: Freeware
Web Site:

Touch Puf is a puzzle game with simple rules, an easy interface, crisp graphics, excellent level design, beautiful backgrounds, and soothing music. What more could you want? The goal of each level to remove all of the colored blocks. You play from a top down perspective, and the game plays as if on ice. Each turn you send a block in any direction and it keeps moving until it hits a wall or another block. If at the end of a turn, two or more blocks of the same color are touching, they "puf" away. You have to figure out how to make all the blocks puf away. This can require very careful planning.

To make things more complicated, many of the levels include special tiles. The arrow tiles, for example, redirect a block passing over it. Beware, you can get into an infinite loop and have to start over. Other special tiles only allow blocks a particular color to pass through; blocks of other colors are reflected. Another special tile changes the color of blocks passing through it. There are transporter tiles and tiles which can only be passed through once. These special tiles add a great deal of depth to the game.

The level design is very good. There are 150 levels. The early levels are easy and introduce the player to the various aspects of the game. Then the levels get progressively more difficult. The later ones are quite challenging. He even plays with you a little bit. Some of the levels include red herrings: special tiles that you think you are going to have to use to solve the level, but in fact do not need. But, none of the levels are unfairly hard. This game is clearly a work of passion by the author.

The game includes a level editor which is easy to use. However, I did not find any user made levels out on the Internet. The game also includes a solution recorder. Solutions for the first 100 levels were recorded by a fan, Michael De Smet, and are available on the Touch Puf website.

I love this game, but I have some nit-picking to do. My first nit is pass codes. After completing each level you are given a pass code to access the next level. This is just plain annoying. To be fair, the game remembers them for you, but if you get stuck on a hard level, you cannot move on and come back later. To be even fairer, the pass codes for the first 100 levels are available on the website. But still, I wish the game just recorded which levels you had completed and allowed you to work on any level.

The second complaint is that the levels are timed. Each level has a time limit. If you do not complete the level within this limit, you have to start over. They do take advantage of this in some levels by introducing special tiles which add or subtract time from the clock. Still, it is not worth it. I like to think and not be rushed. Maybe I am just getting old.

You may notice that the screen shot above says "TIME UNLIMITED". Let me explain. I got so annoyed with the time limit on one level (33 or 34, I forget which) that I busted out my favorite hex editor and looked at the file game.puf. This file contains the starting board for each level. Part of the level info is the time limit encoded as one byte. Well, I changed each to 0x00 which gave me unlimited time for all of the levels. I found this version much more enjoyable. Ok, some of the levels with the special clock tiles became too easy. Any puzzle gamer worth his/her salt should be able to do the same thing if they so desire.

One last thing, there is a bit of confusion over the versions. Version 1.0 contained 100 levels and was available as shareware. You do not want this version. Version 1.5 contains 150 levels, is freeware (thank you), and is the version I played. The website, and several other sites, claim to have version 1.5.5. However, they are all really version 1.5. I think version 1.5.5 was never released.