A nonogram is a picture-based logic puzzle in which the player uses hints on the edge of the puzzle to reveal a picture.

Example of a solved nonogram

Nonograms can either be monochrome or have color groups. Monochrome puzzles are more common, but both are suppported. Color nonograms are represented by IpuzNonogramColor, which is a subclass of IpuzNonogram.

Representation

The IpuzCellType is used to determine whether an IpuzCell is filled in or blank. If it’s a BLOCK, then it’s filled in, while NORMAL indicates a blank cell. A NULL cell could indicate a shaped puzzle, though is not traditionally used with nonograms. In addition, the solution field is set to IpuzPuzzle:block, though can generally be ignored with monochromatic puzzles.

The cell’s IpuzStyle is set by default to a background of black, although puzzle authors can override it.

Other fields in the cell are undefined.

See IpuzNonogramColor for information on how color nonograms are represented.

Guesses

Nonograms use the following convention with an IpuzGuesses struct to record player progress solving a puzzle in its grid:

• A guess of IpuzPuzzle:block is used to indicate a block was guessed correctly. This defaults to the string "#"
• A guess of IpuzNonogram:space is used to indicate that a cell has been eliminated as a possible block. This defaults to the string ".".
• A guess of NULL is used to indicate that the player has yet to determine if a cell is a block or not.

IpuzNonogram also uses the stride_guess of the guesses struct to keep track of whether the cells for the number hints have been found. This is required for nonogram implementations that let the user manually cross off numbers.

The stride guess should be a UTF-8 string with the same number of characters as the number of hints in that row/column. By convention, it uses the IpuzPuzzle:block and IpuzPuzzle:empty properties to indicate if a number has been crossed off or not.

To make it easier to work with the stride, the following convenience functions are provided:

• ipuz_nonogram_set_count_crossed_off()
• ipuz_nonogram_get_count_crossed_off()

Guesses Example

For example, consider the following row being guessed from a nonogram puzzle:

A row guessed from a nonogram

In this example, the guess strings in the row would be set to:

[ NULL, ".", NULL, ".", "#", "#", "#", "#", ".", NULL ]

And the stride_guess for that row would be:

// The stride guesses are 1 and 4 in this example
"0#"

This indicates that the blocks for the number 4 have been found and should be rendered as being eliminated.

Editing

Nonograms have one fix function — ipuz_nonogram_fix_clues(). This should be called after any changes to block polarity or grouping. It will update the internal clues and styles.

Note that not every grid can be uniquely solved as a nonogram. Some nonogram puzzles can result in multiple valid solutions. When creating a nonogram, care must be taken to be sure it’s solvable.