Review: Best Sudoku apps for iPhone and iPod touch

Chances are, you’re fully aware that the number-placement logic game Sudoku is massively popular. But if you’ve been in a cave the past few years and need evidence, look no further than the 18 (and counting) versions of Sudoku apps available in the iTunes App Store, ranging in price from 99 cents to $10.

If you’re a fan of Sudoku, which do you buy? Unfortunately, the current state of the App Store doesn’t allow for demo versions of software, leaving you to take a wild guess based on a short description and a few screenshots. But Macworld is here to help: I tested every iPhone Sudoku app and picked out those worthy of your iPhone’s screen. (It was a tough job, but somebody had to do it.)

Each of the three versions that made it through my screening process, and are covered here, satisfy the following requirements:

• Uses a standard 9-by-9-cell grid of numbers with nine square (3-by-3-cell) regions. (Some Sudoku variants break the standard 9-by-9 grid into non-square geometric areas, or use colors or images instead of numbers.)

• Includes puzzles with only a single solution.

• Provides a way to note (or “pencil in”) the possible values for each square as you solve a puzzle. (These markings are often called notations.)

• Offers good usability: easy-to-use input methods, clear controls, and readable graphics. (For example, a couple Sudoku apps that didn’t make the cut satisfied most criteria, but their methods for making notations obscured other parts of the puzzle.)

• Includes puzzles for multiple skill levels.

Unfortunately, none of the better Sudoku games available for the iPhone and iPod touch exclusively use symmetrical puzzles—those in which the pre-filled boxes (called givens) in opposing regions mirror each other. Although not technically a requirement, many purists don’t consider non-symmetrical puzzles to be “true” Sudoku. I tend to agree, but I didn’t hold a lack symmetry against the candidates. However, I’ve noted in the summaries below if an app uses symmetrical puzzles.

If you’ve never played Sudoku before, I recommend checking out Wikipedia’s page on the game; these reviews assume you know the basics.

Sudoku Vol. 1

Perhaps the best Sudoku app for beginners (and lazy puzzle-solvers), Hudson Entertainment’s Sudoku Vol. 1 offers a tutorial mode that explains Sudoku and walks you through the solving of a puzzle. It also provides a number of visual tools for helping you solve puzzles. For example, one of my favorite “helper” features is called Borders: when you tap on a cell, a gold outline (shown to the right) surrounds the selected cell’s host region and the row and column containing the cell, making it easier to determine which numbers that cell can and cannot contain. (You can turn off this feature if you don’t want it.) In addition, if you double-tap any given cell or solved cell, all other given and solved incidences of that cell’s number are highlighted; this is useful for quickly seeing, for example, which regions still need the number 2. A Hint button, which can be used three times for each puzzle, fills in a random unsolved cell. Finally, when all nine occurrences of a number have been entered, that number is grayed out on the onscreen keypad.

You use this 9-digit keypad to enter notations and cell values. To make notations in a cell, you tap the cell, then tap the notation button, and then tap (on the keypad) the possible values for the cell. To solve a cell, you tap the cell, then tap the solve button, then tap the desired number. (The keypad changes color to indicate whether you’re in notation or solve mode.) There’s also a dedicated erase button, as well as Undo and Redo buttons—the latter two unique to Sudoku Vol. 1. Overall, Sudoku Vol. 1’s controls are excellent, and although the overall appearance of the game isn’t as attractive as that of the other two games here, it’s clear and effective. My only beef is that no matter which font you choose, the numbers used for notations can be difficult to read.

Sudoku Vol. 1 also provides a number of useful customization options. You can choose from six different fonts for numbers (including Japanese Kanji characters) and from six different backgrounds, and the music and sound effects can be separately muted. Other features include a game timer and an online ranking system. But my favorite feature is that the game auto-rotates between portrait and landscape mode, automatically shifting the controls from the bottom (in the former) to the side (in the latter). Unfortunately, the game’s menus for accessing settings are viewable only in portrait mode.

My only major complaint about Sudoku Vol. 1, and one that keeps it from getting a higher rating, is that the game offers only 50 levels, compared to 10,000 for the other two versions covered here. And while the games vary in difficulty, you can’t choose higher levels immediately; you need to solve easier levels to unlock more-difficult ones.

Sudoku Vol. 1’s games are non-symmetrical.

Big Bang Sudoku

The folks at Freeverse have a reputation for producing campy games with attractive visuals, and Big Bang Sudoku is no exception. The shiny, Chiclet-like cells float over a moving background of stars in space, and one of Freeverse’s quirky mascots occasionally pops up to provide feedback on your progress.

You enter notations and cell values using a row of numbers across the bottom of the screen, although the process is different from the one used by Sudoku Vol. 1: First you tap the number you want to enter (1 through 9), then you tap the cell(s) into which you want enter that number. To enter notations, you tap the pencil button at the bottom of the screen to switch to notation mode, then follow the same procedure. (When in notation mode, the pencil button glows orange and each number in the row appears in “notation position,” as shown in the screenshot to the left.)

Although this entry system is simple and understandable, I found it to be a bit of a hassle for entering multiple notations in a single cell; if I wanted, for example, to note that a particular cell could be a 3, 5, or 8, I had to tap 3, then the cell, then 5, then the cell, then 8, and then the cell again. With the input method used by the other two apps covered here, I could simply tap the cell and then tap 3, 5, and 8. On the other hand, if you’re the sort who prefers to first note all cells that could accept a 1, then to note all possible 2s, and so on, this approach is more efficient.

While Big Bang Sudoku doesn’t offer nearly as many options and features as Hudson’s offering, it’s perhaps simpler to use, and it includes over 10,000 puzzles across four difficulty levels (Easy, Medium, Hard, and Diabolical); you can choose your difficulty level at the beginning of each game.

Other features include an option to show all incorrect moves (you can toggle this display on and off, via the Options menu, to quickly view your mistakes); the ability to mute sound; and a game timer. There’s also a stats screen that shows the percentage of puzzles you’ve played that you’ve solved.

Big Bang Sudoku’s games are non-symmetrical.

Sudoku

Electronic Arts (EA) first released a Sudoku game for the 5th-generation iPod back in 2006. The company has updated that game for the iPhone, and except for the fact that you enter numbers using the iPhone’s touchscreen instead of an iPod’s Click Wheel, the gameplay is almost exactly the same. Which is good on two fronts: the original game was pretty good, and the new input method makes the game much more enjoyable.

Like the iPod version, EA’s Sudoku for iPhone offers gorgeous graphics—along with the same lengthy launch and screen-transition times—and 10,000 unique games spanning five difficulty levels (Easy, Normal, Hard, Very Hard, and Insane). You can choose the difficulty level before each game, although you must solve a Hard puzzle to unlock Very Hard, and solve a Very Hard to unlock Insane.

Similar to Big Bang Sudoku, you input numbers using a row of buttons across the bottom of the screen: 1 through 9, along with a separate button to toggle between solving and notating. However, like Sudoku Vol. 1, above, you tap a cell once to highlight it, and then you can tap multiple notations for that cell; I prefer this approach, as it requires less tapping the way I solve puzzles. On the other hand, I did have a few minor complaints about the controls themselves. In addition to the buttons being on the small side, the notation/solve button displays a pen in notation mode and a notation icon in solve mode, which seems backwards to me. The number buttons also appear and disappear as you work with the puzzle. For example, when you solve a cell, the controls disappear and don’t appear again until you tap on an unsolved cell. Although I understand the “contextual” theory behind this approach, I found it slowed down gameplay as I had to wait for the controls to fade in each time I tapped on an unsolved cell.

When solving puzzles, an error-checking option can identify incorrect cell values, and a hint feature solves the “easiest” unsolved cell (or corrects the easiest mistake). As with Sudoku Vol. 1, tapping on a solved or given cell highlights all other cells containing that solved or given number. Another nifty feature is Auto-Fill, which automatically fills the notations for all empty cells. Although useful as an aid in solving a puzzle, it’s also a convenient way to speed up a game: with all notations filled in, you can jump ahead to using logic to actually solve the puzzle. And with the iPhone version of the game, you can activate Auto-Fill by shaking the iPhone vigorously!

One other great feature offered by EA Sudoku is Newspaper mode, which lets you manually enter and play puzzles from a newspaper, Sudoku book, or online game. If you’re feeling adventurous, you can even use this mode to create your own Sudoku puzzles; a validation feature will tell you if your homemade puzzle works.

EA has included detailed, text-based help that explains the rules of the game as well as all options. You also get statistics on your progress, as well as a scoring system that awards points for solving puzzles, reducing the points earned when you use hints and the error-checking feature. You can toggle music and sound effects on and off separately, as well as adjust the overall audio volume within the game.

EA Sudoku’s games are non-symmetrical at higher difficulty levels.

Cream of the Sudoku crop

So which do you choose? If you notate your puzzles by entering all possible occurrences of each digit at once—for example, all cells that could contain a 3—Big Brain Sudoku’s entry method is the best of the bunch. Otherwise, the offerings from EA and Hudson Entertainment offer more features and options. The Hudson version is the most full-featured and provides more assistance for learning the game; it’s too bad it doesn’t include more unique puzzles. EA’s offering is visually appealing and its 10,000 puzzles should keep you busy for a long, long time. You can’t go wrong with any of the three.

All games are compatible with any iPhone or iPod touch running iPhone 2.0 software.

Update 2008/07/16 3:20pm: Another Sudoku app, Satori Sudoku, was cut from my list of “best” apps because of one fatal flaw: it produced puzzles with multiple solutions. (Sudoku games, by definition, can have only a single solution.) The developer of Satori Soduku has told several Macworld readers that this bug has been fixed in an updated version of Satori Sudoku, which should be available through the App Store in the next few days. If so, I recommend checking it out, as well—it’s otherwise comparable in quality to the three games reviewed here.