Puzzle

How to solve color nonograms

Color nonograms (picross, griddlers, paint by numbers puzzles) in a few minutes: the rules, the first moves and the main techniques. Try it on a 5×5 heart.

The rules

A nonogram is a grid with numbers by every row and column. Each number is a run: so many cells of its color in a row. The runs go in the order of the numbers.

In a color nonogram the numbers have colors. Two runs of the same color always have at least one empty cell between them; runs of different colors may stand right next to each other — that is what makes color nonograms friendlier than black-and-white ones.

When every row and column matches its numbers, the picture is done. Every puzzle here has exactly one solution, and it can be found by logic alone.

The first moves

Big numbers first. A run of 8 in a line of 10 can start at cell 1 at the earliest and at cell 3 at the latest: cells 3 to 8 are filled either way. This is the overlap — the most useful move of all.

Full lines. If the runs with their gaps add up to the length of the line, the whole line is known at once.

Mark what is empty. When a line matches its numbers, put ✕ in the rest. Crosses help the crossing lines.

Techniques for colors

Touching colors. A red 3 followed by a blue 2 needs no gap: knowing where the red ends tells you where the blue begins.

Colors that cannot be there. If a column has no green at all, no cell of that column can be green: every green run of a crossing row must avoid it.

The edges. A filled cell next to the border is the start of the first run of its color in that line.

When you are stuck

Look for the line with the fewest possibilities: the shortest gaps, the biggest numbers. Use «Check» to see mistakes, «Hint» to open one cell — both are honest, and the result shows the hints.