How to play Nonograms

Every row and every column carries a label: the lengths of its blocks of filled cells, written in the order they occur, with at least one empty cell between one block and the next. A line labelled “4 2” holds a block of four, then a gap, then a block of two — in that order, reading left to right or top to bottom.

Work out which cells are filled and a drawing comes out. The labels are the puzzle; on the rare picture where they are not quite enough, a square starts filled in for you.

The first move: overlap

This is the technique that opens almost every board. Take a row of five cells labelled “4”.

Five cells, and a single run of four somewhere in them.

The run of four can start at the first cell or the second, and nowhere else. Slide it to the far left and it covers cells one to four; slide it to the far right and it covers cells two to five. You do not know which, and you do not need to: cells two, three and four are covered either way.

So those three can be filled in with certainty, before you know where the run begins. That is overlap, and on a twenty-wide grid it fills a great deal of the board in the first few minutes.

The other half: crossing out

Marking a cell you have ruled out is not bookkeeping; it is half the game. A crossed cell ends a block, and ending a block is what lets you count the next one from a fixed edge instead of from a guess.

Once a line's runs are all placed, every remaining cell in it can be crossed at once. Do that, and the columns crossing it suddenly have hard edges to count from. Most of the middle of a nonogram is this, back and forth: a row gives a column an edge, the column gives two rows an edge.

Line logic is always enough

Every board here can be solved one line at a time. You are never required to play a cell speculatively and see what breaks, or to hold two rows against each other and hope. If a line can be advanced at all, it can be advanced from its own numbers and what is already on the grid.

Where the difficulty actually comes from

Easy and Medium are ten by ten and fifteen by fifteen, where the size is the difficulty. Hard and Master are both twenty by twenty, and size is not what separates them. On Master there are at least two moments where no line near you will move on its own and you have to hunt elsewhere on the grid for the next foothold. On Hard there are none.

Playing here

Fill the cells you are sure of, and cross out the ones you have ruled out. Dragging across a run marks the whole run at once. When a line is finished — every one of its runs in place — that line's whole set of clue numbers dims, so what is left on the board is what is still lit.

Play Nonograms