Kim did it again …

In my earlier post on Vexed I mentioned the Vexed-clone by the korean developer Kim Byung Kwon. I was highly critical of that app because Kim did not refer to the GNU-license of the original game by James McCombe. Now, it turns out (as discussed in the comments to that post) that James McCombe was possibly not the true originator of that puzzle anyway.

However, Kim did it again, though this time with sliding block puzzles! He simply copied some of the best sliding block puzzles from Nick Baxter’s Sliding Block Page and now sells them for one dollar as Sliding Puzzle (iTunes link), without any mention of the originators! Let me rectify this at least here: the puzzles shown on the screenshot in iTunes are by Junichi Yananose, Serhiy Grabarchuk, Minoru Abe, and Ed Pegg Jr.

Kim’s webpage is difficult to decifer (neither my nor google’s knowledge of Korean is sufficient to really make sense of this page). If somebody know how to contact this person, please let me know. I find this unacceptable.

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Please acknowledge the designer!

The point of copyright and intellectual property for puzzle designs already came up in passing in my posts about to Rush Hour and Lunar Lockout. However, today an even more obvious problem arose in the app store: Blockade (link redirects to iTunes). This gives me the possibility to very clearly and forcefully explain to all developers out there:  

• Puzzle-designs are intellectual property of the designer.
• Even if they are available online, please ask the designer when you want to use the puzzle.
  
• Don’t be afraid: most will be thrilled and extremely cooperative.
  
• And most importantly: mention the name of the designer clearly alongside each individual puzzle!

Re-Shuffling Rush Hour

A sliding block puzzle is normally played inside a tray, in which the block can move around orthogonally. How about other possibilities of moving block around? Enter Subway Shuffle: Rush Hour on a graph. Or, as the developer Bob Hearn explains it:

Imagine playing Rush Hour, but make all the cars 1×1 instead of 1×2 or 1×3. But still some can only move vertically, others horizontally. Replace the cars by tokens, red for horizontal, blue for vertical, and put the tokens on nodes of a graph with colored edges: red tokens can only move on red edges, blue on blue. If you use a grid graph, with horizontal edges red and vertical edges blue, then you have 1×1 Rush Hour. If you relax the grid graph constraint, and also allow more colors, then you get Subway Shuffle. These relaxations allow for lots of interesting possibilities in puzzle configuration. It’s also possible to have extremely complicated puzzles in a very small space: I’ve generated some puzzles on small graphs that require over 1,000 moves.

Know How to extend Rush Hour

Things move fast in the app store. I just wrote this summary on Rush Hour puzzles, and then today a new variation becomes available: Know How [iTunes Link]. I have not bought the game (at 3€ I find it too expensive to try it out; hopefully a lite version will become available soon). However, from the description and the other information on the web it is clearly a Rush Hour variant. The block can only slide in the direction of the elongation, and the treasure box has to be moved out to a destination outside the playing field (at the bottom in the screen shot to the right).

Rush Hour

One approach to make sliding block puzzles more complicated is by restricting the movements of the blocks. The most prominent example of this strategy is Rush Hour. In this puzzle, all sliding blocks are rectangles of size nx1. These blocks can only be moved in the direction of the elongation. The original trick to make this restriction transparent to the user is to show the block as cars (hence the name “Rush Hour”). It is then immediately obvious that the car can only be moved forwards or backwards, and not sideways.

Rush hour was invented by Nobuyuki “Nob” Yoshigahara and marketed as a physical puzzle by ThinkFun (formerly Binary Arts). There are at least four implementations of Rush Hour available in the app store (links redirect to iTunes):

Toroidal sliding block puzzles

A new variation on the sliding block theme was recently introduced in the app store: sliding blocks on a torus! Of course, the marketing of the puzzles do not call it like that, but it actually is a nice further development, which uses the possibilities of the touch screen to produce a puzzle variation that is not easily reproduced in a physical puzzle.

So, what is a toroidal sliding block puzzle? Well, the basic idea is that the left and the right sides of the puzzle are connected, and likewise the top and the bottom sides. When you slide something off the top, it will reappear on the bottom, and likewise for the other sides. Mathematically speaking, this means that the pieces are sliding on a torus.

Pennant-like sliding block puzzles

After the 1880’s craze of the 15-puzzle (see the previous post) developments lay still for a few decades. The next development was a sliding block puzzle adding larger blocks of sizes 1×2 and 2×2, and enlarging the tray from 4×4 to 4×5. The first such puzzle was patented in 1907 by L. W. Hardy (U.S. Patent 1,017,752, patent granted 1912) and copyrighted on the name ‘Pennant puzzle’ in 1909. The goal of this puzzle is to move the 2×2 piece to a predetermined position on the bottom of the tray.

This puzzle is one of the most widely commercialized puzzles in the world, existing in dozen of variants. Likewise, there are at least seven implementations of this puzzle available in the app store (links redirect to iTunes Store):

A primer on sliding block puzzles

Given the gorgeous touch screen it has, the iPhone is destined to be used for sliding block puzzles. Edward Hordern, the grandmaster of sliding block puzzles defined these kind of puzzles as follows:

“A sliding block puzzle consists of a group of pieces of any shape(s) enclosed within a confined area, in which the purpose is to rearrange the pieces either into a certain order or to get a particular piece to a specified position. This is accomplished by sliding the pieces or “blocks” —hence the name sliding block puzzles — usually one at a time into areas not occupied by other pieces. The lifting of pieces is never allowed — nor must they hop or jump over other pieces.”

Edward Hordern’s classic 1986 volume on these puzzles ‘Sliding Piece Puzzles’ is unfortunately long out of print, but a selection of the wide array of puzzles that have been develop in this realm can be found on Nick Baxter’s Sliding block page on PuzzleWorld and Rob Stegmann’s Sliding Block page.