How to solve a nonogram

A nonogram is a grid with numbers beside each row and above each column. The numbers say how long each run of filled squares is, in order. “3 1” means a run of three, at least one empty square, then a run of one. When every row and column matches its numbers, a picture appears.

Controls

• Fill and Cross choose what a tap does. Tap a square again to clear it.
• Drag across a row or column to mark several squares at once. The drag stays in a straight line.
• On a keyboard: arrow keys move, Space uses the current tool, F fills, X crosses out, Ctrl or Cmd + Z undoes.
• Clues turn pale once their line matches. That tells you the line is done, not that it is right, so keep an eye on the crossing lines.

Five techniques

1. Big runs cover the middle

In a line of 10, a run of 7 must cover squares 4 to 7 wherever it sits. Slide the run as far left as it goes, then as far right; the squares both positions share are filled. This works for several runs at once too.

2. Lines that add up

Add the runs and one gap between each. If the total equals the line length, there is only one way to place them. “4 5” in a line of 10 is exactly that.

3. Edges push runs

A filled square against the border must be the start of the first run. If the first clue is 3, the next two squares are filled and the one after is empty.

4. Gaps that are too small

A space between crosses that is shorter than every run that could go there must be empty. Cross it out.

5. Finish lines, then look across

When a row is complete, cross out its remaining squares. Each new square you settle belongs to a column too, so read that column again. Most puzzles are solved by going back and forth like this.

Questions

What is a nonogram?

A grid puzzle where numbers beside each row and above each column tell you the lengths of the filled runs in that line. Filling the grid correctly reveals a picture.

Do nonograms need guessing?

Good ones do not. Every puzzle on Nonogram Today can be finished with logic alone, and has exactly one answer.

What do the crosses do?

A cross marks a square you know is empty. It does not change the answer, but it keeps track of what you have proved, which makes the next deduction easier.

What are nonograms also called?

Hanjie, griddlers, paint by numbers, picture cross, pic-a-pix and logic art are all names for the same kind of puzzle.

Play today's puzzle or start small with a 5 by 5 practice grid.