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

When used with an IpuzGuesses object, guesses are tested against the string IpuzPuzzle:block to indicate a block was guessed correctly. Since implementations will want to record additional information per-cell, any other guess string will be ignored.

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.