Sokoban: not just sliding, but pushing blocks

In his classic definition of Sliding Block puzzles, Edward Horden explicitly noted that “there must be no requirement that they be pushed or pulled by other pieces.” So, let’s change the topic from sliding blocks (as discussed in the last few posts) to pushing blocks.

The most well-known instantiation of a pushing block puzzle is Sokoban (Japanese for ‘warehouse keeper’), created in 1980 by Hiroyuki Imabayashi. In this puzzle, various blocks must be pushed to their destination in a twisted warehouse. The blocks cannot be pulled, so when a block is pushed into a corner it is stuck, and eventually the puzzle will have to be restarted.

There are currently six implementations of Sokoban available in the app store (links redirect to iTunes):

• BoxMan
• Smart Sokoban [Free version]
• Naboko [Free version]
• iSoko Sokoban
• Apple Push
• Rabbit Run [Free version]

Although Sokoban puzzles are really abstract sequential movements puzzles (doing things in the wrong order will get you in trouble), the metaphor of a warehouse keeper is very suitable. There is always one block (the ‘keeper’) that can push the other blocks. One of the blocks is an agent, the other are passive blocks, so to speak. A good design makes this difference obvious to the user. For that reason, I don’t really like an implementation like Smart Sokoban (shown to the right), because the agent is only differentiated in color and shape. As many of the other implementations show, it is much better to add some more agent-like figure (rabbits anyone?) and/or some animations (for example, in Naboko the eyes of the pusher are blinking).

Overall, I am particularly intrigued by the implementation as offered by Naboko (see illustration to the right). The graphics are polished, the keeper is decently animated, there are nice zooming possibilities, and the names of the designers are well documented with all levels. However, the most important feature is the innovative control-system. Sokoban puzzles tend to become a bit tedious because many movements are necessary for the more interesting puzzles. In Naboko, many of these movements are done automatically, which make you focus more on solving the actual problems, and not on moving of the warehouse keeper.

The trick of Naboko is that you select the box you want to move (I have selected the block in the upper right of the illustration), and then it shows you all positions you can reach with only straight pushes (shown by blue circles). Clicking on any of these destinations makes the keeper immediately do all the moves for you. For example, moving the block to the blue circle under the keeper in the illustration to the right will normally take six movements. In Naboko is it only one click!

[Update 7 december 2008] A new version became available: 3D Sokoban. I didn’t try it out myself (not again…), but from the description it becomes clear that it is just a basic sokoban implementation with a twist to get it more difficult for the user: you can see the configuration from a top-down perspective (as in classic sokoban), but you can only move the pieces in a 3D perspective looking through the eyes of the warehouse keeper! To me that just seems to be tedious. I would have found it a much more interesting development if the developer would have left out the top-down version. Why not take a selection of relatively easy sokoban puzzles, but only show them through the perspective of the pusher. Then the puzzle would also involve reconstructing the lay-out of the rooms and the position from the crates. That would be the same difficulty that made the original Chip’s Challenge challenging.

[Update 22 February 2009] A new Sokoban implementation became available: Crate Maze. Don’t believe the developer that this is an “ancient Chinese problem solving puzzle game”. You know better now…

[Update 22 February 2009] Also new is ChocoBan. This one actually sounds interesting, because it adds a new dimension to classical sokoban. Instead of just one type of crate, in ChocoBan there are two kinds of chocolates, namely square ones and round ones. They have to be pushed to their respective square and round goals. Now, the interesting aspect of the original Sokoban was of course that you have to figure out which crate should go where, and good levels actually have a one-to-one correspondence between crates and goals. So, I doubt that ChocoBan really presents a much different gameplay—I expect that it will be simpler than classic sokoban. However, it might be easier to make difficult levels on a small game board. Currently the game won’t run on my first generation iPod Touch, so I can’t tell you more yet.

[Update 2 March 2009] Next Sokoban clone: Tomato Boxes. Says to include an impressive number of 13.000 levels (my favorite Naboko only has 2.500, although that seems sufficient as well). From the screenshots it looks as if the sources of the levels are indicated. Hopefully with complete names.

[Update 11 March 2009] I finally had the possibility to try ChocoBan, as screenshot of which is shown to the left here. It is a fine Sokoban implementation with a shortcut-option in which you can indicate the block to be pushed, and the Bunny will then do the rest automatically (almost like in Naboko). However, as I feared (see my earlier comment above), the distinction between round and square blocks does not really add something (at least not in the current levels). The level shown here to the left is actually pretty challenging for such a small size, but the blocks might just as well all identical for the difficulty to be the same. Still: worth a try (even more so given the price ).

[Update 27 March 2009] Sokoban in an isometric projection: Ankagua3D. Looks nice, but sokoban is not about the looks…

[Update 28 March 2009 ] Shape Escape and Shape Escape Lite (shown to the right) take the principle from ChocoBan one step further. Shape Escape is Sokoban in which the blocks have three different colors and two different shapes, and the goals for these blocks are marked accordingly. However, Shape Escape makes solving the puzzles easier because rightly placed blocks vanish. The only complication is that you are not allowed to push the wrong colored block on a goal—you will have start over when you do this (no undo…). And then there is an inexplicable time limit: good puzzles don’t need a time limit—only poor puzzles need a time limit to artificially raise the difficulty.

[Update 31 March 2009] Chicken Push (Sokoban)

[Update 5 April 2009] Snap it

[Update 7 May 2009] Sokoban with a few extras (switches and force fields): Boxed In. Looks nice. Anybody tried it?

[Update 7 May 2009] Classic Sokoban, and it doesn’t even look good: iBoxes

[Update 31 May 2009] Pocoman Libre.

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