solo(6) puzzle game based on Sudoku

## SYNOPSIS

solo [--generate n] [--print wxh [--with-solutions] [--scale n] [--colour]] [game-parameters|game-ID|random-seed]

solo --version

## DESCRIPTION

You have a square grid, which is divided into as many equally sized sub-blocks as the grid has rows. Each square must be filled in with a digit from 1 to the size of the grid, in such a way that

• every row contains only one occurrence of each digit
• every column contains only one occurrence of each digit
• every block contains only one occurrence of each digit.
• (optionally, by default off) each of the square's two main diagonals contains only one occurrence of each digit.

You are given some of the numbers as clues; your aim is to place the rest of the numbers correctly.

Under the default settings, the sub-blocks are square or rectangular. The default puzzle size is 3×3 (a 9×9 actual grid, divided into nine 3×3 blocks). You can also select sizes with rectangular blocks instead of square ones, such as 2×3 (a 6×6 grid divided into six 3×2 blocks). Alternatively, you can select ‘jigsaw’ mode, in which the sub-blocks are arbitrary shapes which differ between individual puzzles.

Another available mode is ‘killer’. In this mode, clues are not given in the form of filled-in squares; instead, the grid is divided into ‘cages’ by coloured lines, and for each cage the game tells you what the sum of all the digits in that cage should be. Also, no digit may appear more than once within a cage, even if the cage crosses the boundaries of existing regions.

If you select a puzzle size which requires more than 9 digits, the additional digits will be letters of the alphabet. For example, if you select 3×4 then the digits which go in your grid will be 1 to 9, plus ‘a’, ‘b’ and ‘c’. This cannot be selected for killer puzzles.

I first saw this puzzle in Nikoli (http://www.nikoli.co.jp/puzzles/1/index_text-e.htm), although it's also been popularised by various newspapers under the name ‘Sudoku’ or ‘Su Doku’. Howard Garns is considered the inventor of the modern form of the puzzle, and it was first published in Dell Pencil Puzzles and Word Games. A more elaborate treatment of the history of the puzzle can be found on Wikipedia (http://en.wikipedia.org/wiki/Sudoku).

## Solo controls

To play Solo, simply click the mouse in any empty square and then type a digit or letter on the keyboard to fill that square. If you make a mistake, click the mouse in the incorrect square and press Space to clear it again (or use the Undo feature).

If you right-click in a square and then type a number, that number will be entered in the square as a ‘pencil mark’. You can have pencil marks for multiple numbers in the same square. Squares containing filled-in numbers cannot also contain pencil marks.

The game pays no attention to pencil marks, so exactly what you use them for is up to you: you can use them as reminders that a particular square needs to be re-examined once you know more about a particular number, or you can use them as lists of the possible numbers in a given square, or anything else you feel like.

To erase a single pencil mark, right-click in the square and type the same number again.

All pencil marks in a square are erased when you left-click and type a number, or when you left-click and press space. Right-clicking and pressing space will also erase pencil marks.

Alternatively, use the cursor keys to move the mark around the grid. Pressing the return key toggles the mark (from a normal mark to a pencil mark), and typing a number in is entered in the square in the appropriate way; typing in a 0 or using the space bar will clear a filled square.

(All the actions described below are also available.)

## Solo parameters

Solo allows you to configure two separate dimensions of the puzzle grid on the ‘Type’ menu: the number of columns, and the number of rows, into which the main grid is divided. (The size of a block is the inverse of this: for example, if you select 2 columns and 3 rows, each actual block will have 3 columns and 2 rows.)

If you tick the ‘X’ checkbox, Solo will apply the optional extra constraint that the two main diagonals of the grid also contain one of every digit. (This is sometimes known as ‘Sudoku-X’ in newspapers.) In this mode, the squares on the two main diagonals will be shaded slightly so that you know it's enabled.

If you tick the ‘Jigsaw’ checkbox, Solo will generate randomly shaped sub-blocks. In this mode, the actual grid size will be taken to be the product of the numbers entered in the ‘Columns’ and ‘Rows’ boxes. There is no reason why you have to enter a number greater than 1 in both boxes; Jigsaw mode has no constraint on the grid size, and it can even be a prime number if you feel like it.

If you tick the ‘Killer’ checkbox, Solo will generate a set of of cages, which are randomly shaped and drawn in an outline of a different colour. Each of these regions contains a smaller clue which shows the digit sum of all the squares in this region.

You can also configure the type of symmetry shown in the generated puzzles. More symmetry makes the puzzles look prettier but may also make them easier, since the symmetry constraints can force more clues than necessary to be present. Completely asymmetric puzzles have the freedom to contain as few clues as possible.

Finally, you can configure the difficulty of the generated puzzles. Difficulty levels are judged by the complexity of the techniques of deduction required to solve the puzzle: each level requires a mode of reasoning which was not necessary in the previous one. In particular, on difficulty levels ‘Trivial’ and ‘Basic’ there will be a square you can fill in with a single number at all times, whereas at ‘Intermediate’ level and beyond you will have to make partial deductions about the set of squares a number could be in (or the set of numbers that could be in a square). At ‘Unreasonable’ level, even this is not enough, and you will eventually have to make a guess, and then backtrack if it turns out to be wrong.

Generating difficult puzzles is itself difficult: if you select one of the higher difficulty levels, Solo may have to make many attempts at generating a puzzle before it finds one hard enough for you. Be prepared to wait, especially if you have also configured a large puzzle size.

## Common actions

These actions are all available from the ‘Game’ menu and via keyboard shortcuts, in addition to any game-specific actions.

(On Mac OS X, to conform with local user interface standards, these actions are situated on the ‘File’ and ‘Edit’ menus instead.)

New game (‘N’, Ctrl+‘N’)
Starts a new game, with a random initial state.
Restart game
Resets the current game to its initial state. (This can be undone.)
Loads a saved game from a file on disk.
Save
Saves the current state of your game to a file on disk.

The Load and Save operations preserve your entire game history (so you can save, reload, and still Undo and Redo things you had done before saving).

Print
Where supported (currently only on Windows), brings up a dialog allowing you to print an arbitrary number of puzzles randomly generated from the current parameters, optionally including the current puzzle. (Only for puzzles which make sense to print, of course – it's hard to think of a sensible printable representation of Fifteen!)
Undo (‘U’, Ctrl+‘Z’, Ctrl+‘_’)
Undoes a single move. (You can undo moves back to the start of the session.)
Redo (‘R’, Ctrl+‘R’)
Redoes a previously undone move.
Copy
Copies the current state of your game to the clipboard in text format, so that you can paste it into (say) an e-mail client or a web message board if you're discussing the game with someone else. (Not all games support this feature.)
Solve
Transforms the puzzle instantly into its solved state. For some games (Cube) this feature is not supported at all because it is of no particular use. For other games (such as Pattern), the solved state can be used to give you information, if you can't see how a solution can exist at all or you want to know where you made a mistake. For still other games (such as Sixteen), automatic solution tells you nothing about how to get to the solution, but it does provide a useful way to get there quickly so that you can experiment with set-piece moves and transformations.

Some games (such as Solo) are capable of solving a game ID you have typed in from elsewhere. Other games (such as Rectangles) cannot solve a game ID they didn't invent themself, but when they did invent the game ID they know what the solution is already. Still other games (Pattern) can solve some external game IDs, but only if they aren't too difficult.

The ‘Solve’ command adds the solved state to the end of the undo chain for the puzzle. In other words, if you want to go back to solving it yourself after seeing the answer, you can just press Undo.

Quit (‘Q’, Ctrl+‘Q’)
Closes the application entirely.

## Specifying games with the game ID

There are two ways to save a game specification out of a puzzle and recreate it later, or recreate it in somebody else's copy of the same puzzle.

The ‘Specific’ and ‘Random Seed’ options from the ‘Game’ menu (or the ‘File’ menu, on Mac OS X) each show a piece of text (a ‘game ID’) which is sufficient to reconstruct precisely the same game at a later date.

You can enter either of these pieces of text back into the program (via the same ‘Specific’ or ‘Random Seed’ menu options) at a later point, and it will recreate the same game. You can also use either one as a command line argument (on Windows or Unix); see below for more detail.

The difference between the two forms is that a descriptive game ID is a literal description of the initial state of the game, whereas a random seed is just a piece of arbitrary text which was provided as input to the random number generator used to create the puzzle. This means that:

Descriptive game IDs tend to be longer in many puzzles (although some, such as Cube (cube(6)), only need very short descriptions). So a random seed is often a quicker way to note down the puzzle you're currently playing, or to tell it to somebody else so they can play the same one as you.
Any text at all is a valid random seed. The automatically generated ones are fifteen-digit numbers, but anything will do; you can type in your full name, or a word you just made up, and a valid puzzle will be generated from it. This provides a way for two or more people to race to complete the same puzzle: you think of a random seed, then everybody types it in at the same time, and nobody has an advantage due to having seen the generated puzzle before anybody else.
It is often possible to convert puzzles from other sources (such as ‘nonograms’ or ‘sudoku’ from newspapers) into descriptive game IDs suitable for use with these programs.
Random seeds are not guaranteed to produce the same result if you use them with a different version of the puzzle program. This is because the generation algorithm might have been improved or modified in later versions of the code, and will therefore produce a different result when given the same sequence of random numbers. Use a descriptive game ID if you aren't sure that it will be used on the same version of the program as yours.

(Use the ‘About’ menu option to find out the version number of the program. Programs with the same version number running on different platforms should still be random-seed compatible.)

A descriptive game ID starts with a piece of text which encodes the parameters of the current game (such as grid size). Then there is a colon, and after that is the description of the game's initial state. A random seed starts with a similar string of parameters, but then it contains a hash sign followed by arbitrary data.

If you enter a descriptive game ID, the program will not be able to show you the random seed which generated it, since it wasn't generated from a random seed. If you enter a random seed, however, the program will be able to show you the descriptive game ID derived from that random seed.

Note that the game parameter strings are not always identical between the two forms. For some games, there will be parameter data provided with the random seed which is not included in the descriptive game ID. This is because that parameter information is only relevant when generating puzzle grids, and is not important when playing them. Thus, for example, the difficulty level in Solo (above) is not mentioned in the descriptive game ID.

These additional parameters are also not set permanently if you type in a game ID. For example, suppose you have Solo set to ‘Advanced’ difficulty level, and then a friend wants your help with a ‘Trivial’ puzzle; so the friend reads out a random seed specifying ‘Trivial’ difficulty, and you type it in. The program will generate you the same ‘Trivial’ grid which your friend was having trouble with, but once you have finished playing it, when you ask for a new game it will automatically go back to the ‘Advanced’ difficulty which it was previously set on.

The ‘Type’ menu, if present, may contain a list of preset game settings. Selecting one of these will start a new random game with the parameters specified.

The ‘Type’ menu may also contain a ‘Custom’ option which allows you to fine-tune game parameters. The parameters available are specific to each game and are described in the following sections.

## Specifying game parameters on the command line

(This section does not apply to the Mac OS X version.)

The games in this collection deliberately do not ever save information on to the computer they run on: they have no high score tables and no saved preferences. (This is because I expect at least some people to play them at work, and those people will probably appreciate leaving as little evidence as possible!)

However, if you do want to arrange for one of these games to default to a particular set of parameters, you can specify them on the command line.

The easiest way to do this is to set up the parameters you want using the ‘Type’ menu (see above), and then to select ‘Random Seed’ from the ‘Game’ or ‘File’ menu (see above). The text in the ‘Game ID’ box will be composed of two parts, separated by a hash. The first of these parts represents the game parameters (the size of the playing area, for example, and anything else you set using the ‘Type’ menu).

If you run the game with just that parameter text on the command line, it will start up with the settings you specified.

For example: if you run Cube (see cube(6)), select ‘Octahedron’ from the ‘Type’ menu, and then go to the game ID selection, you will see a string of the form ‘o2x2#338686542711620’. Take only the part before the hash (‘o2x2’), and start Cube with that text on the command line: ‘cube o2x2’.

If you copy the entire game ID on to the command line, the game will start up in the specific game that was described. This is occasionally a more convenient way to start a particular game ID than by pasting it into the game ID selection box.

(You could also retrieve the encoded game parameters using the ‘Specific’ menu option instead of ‘Random Seed’, but if you do then some options, such as the difficulty level in Solo, will be missing. See above for more details on this.)

## Unix command-line options

(This section only applies to the Unix port.)

In addition to being able to specify game parameters on the command line (see above), there are various other options:

--game

These options respectively determine whether the command-line argument is treated as specifying game parameters or a save file to load. Only one should be specified. If neither of these options is specified, a guess is made based on the format of the argument.
--generate n
If this option is specified, instead of a puzzle being displayed, a number of descriptive game IDs will be invented and printed on standard output. This is useful for gaining access to the game generation algorithms without necessarily using the frontend.

If game parameters are specified on the command-line, they will be used to generate the game IDs; otherwise a default set of parameters will be used.

The most common use of this option is in conjunction with --print, in which case its behaviour is slightly different; see below.

--print wxh
If this option is specified, instead of a puzzle being displayed, a printed representation of one or more unsolved puzzles is sent to standard output, in PostScript format.

On each page of puzzles, there will be w across and h down. If there are more puzzles than w×h, more than one page will be printed.

If --generate has also been specified, the invented game IDs will be used to generate the printed output. Otherwise, a list of game IDs is expected on standard input (which can be descriptive or random seeds; see above), in the same format produced by --generate.

For example:

```net --generate 12 --print 2x3 7x7w | lpr
```

will generate two pages of printed Net puzzles (each of which will have a 7×7 wrapping grid), and pipe the output to the lpr command, which on many systems will send them to an actual printer.

There are various other options which affect printing; see below.

--save file-prefix [ --save-suffix file-suffix ]
If this option is specified, instead of a puzzle being displayed, saved-game files for one or more unsolved puzzles are written to files constructed from the supplied prefix and/or suffix.

If --generate has also been specified, the invented game IDs will be used to generate the printed output. Otherwise, a list of game IDs is expected on standard input (which can be descriptive or random seeds; see above), in the same format produced by --generate.

For example:

```net --generate 12 --save game --save-suffix .sav
```

will generate twelve Net saved-game files with the names game0.sav to game11.sav.

--version
Prints version information about the game, and then quits.

The following options are only meaningful if --print is also specified:

--with-solutions
The set of pages filled with unsolved puzzles will be followed by the solutions to those puzzles.
--scale n
Adjusts how big each puzzle is when printed. Larger numbers make puzzles bigger; the default is 1.0.
--colour
Puzzles will be printed in colour, rather than in black and white (if supported by the puzzle).