Domain of the Bored

A couple of weeks ago, I posted a list of requirements for an iPhone sudoku app. At the time, no app satisfied all of the requirements, but one did come close.

Pierre Bernard of Houdah Software posted a comment that his sudoku app, ACTSudoku, satisfied all but one of the requirements I listed. The only one remaining was rotational symmetry, which he asked about.

In response to our dialog on that post, he added rotational symmetry in ACTSudoku 1.1, which Apple has now approved. You can download it now for $2.99 USD (or free if you bought one of the earlier versions).

UPDATE 2008-08-01: As of yesterday, there's now a free version of ACTSudoku, which only generates easy puzzles. This is good if you'd like to try it for yourself, but you don't want to spend $3 just yet.

The interface is simple enough:

Notice that there's no row of numbers for input. The obvious thing to try is tap on a cell, and it works:

In other words, the interface is obviously postfix. The key word there is “obviously”: One of my requirements was that it must be obvious how to input numbers.

The input method is not perfectly obvious, however. One thing that stumps a lot of people (going by Bernard's response to some iTunes reviews) is the fact that simply tapping on a number in the pop-up enters a pencil-mark, rather than locking in the number. You must hold down briefly to set a number in the cell. In the comments on the previous post, I suggested swapping these behaviors; I maintain that suggestion. (UPDATE 2008-10-29: ACTSudoku 1.5 added a preference to do this. It does, indeed, make a tremendous difference in the app's usability.)

You may be wondering what all the green dots are. Those are pencil-marks, filled in automatically by the game. This is optional; you can turn it off in the settings, if you want to be completely free to make mistakes.

With the automatic pencil-marks turned on, the game will not let you enter a wrong number. With them turned off, the game will let you enter a wrong number. Either way, you can clear the cell by tapping again on the cell and holding down on the giant number.

Hold down on that giant 4 to clear it from the cell.

Of course, ACTSudoku is not perfect. It has some minor problems:

• The interface confusion that I noted above. A long tap sets the number, whereas a short tap sets a pencil-mark. This arrangement makes no sense with automatic pencil-marks turned on—and they're on by default. It would make much more sense to have the tap lengths the other way around.
• The northern, eastern, southern, and western blocks are have dimmed-looking gray backgrounds, for no apparent reason. This is slightly distracting (but not enough to qualify as “garish”). I would prefer if all the blocks were uniform white.
• I'd like to be able to turn off the timer. Again, I find this distracting.

However, it satisfies all of my requirements, so I declare ACTSudoku the winner of the iPhone sudoku race. Congratulations to Houdah Software!

• A sudoku generator. The game should not cap me at x-hundred or x-thousand puzzles. Give me all the sudoku the iPhone OS' PRNG can create for me.

• Proper sudoku puzzles, not Number Place puzzles. The difference is that a sudoku puzzle is rotationally symmetric: if you turn the puzzle 180°, it still looks the same.

  → 180° →

  Many sudoku generators actually generate Number Place puzzles, which don't have this constraint. (In particular, all the Will Shortz puzzles are like this.)

• Obvious input method. A row of numbers at the bottom doesn't work because I can't tell whether the game is prefix (tap number first, then cell) or postfix (tap cell first, then number). I could get used to either way, but a good interface doesn't make me guess.

  • Ambrosia's Mr. Sudoku uses handwriting recognition.

  • Platinum Sudoku is clearly postfix, because its input method is a ring of numbers around whatever cell you tap on.

• The ability to set pencilmarks, to keep track of what numbers are viable for a cell (helping to avoid wrong numbers, especially at higher difficulty levels).

• Simple, usable interface. This means two things:

  • No excessive artwork like Big Bang Sudoku has. I only have 16 GB of flash memory—don't waste it!

  • No garish colors. If your sudoku game is in CGA, then I don't want to look at it, which means I don't want to play it, which means I don't want to buy it.