Controls

You play in two modes, switched with the Fill/Mark button above the board. Filling a cell and marking it as empty are two separate actions, not two taps on the same cell.

The numbers before each row and column list the lengths of the filled blocks in order, with at least one empty cell between each block. A clue of '3 1' means a run of three, a gap, then a single filled cell.

• Fill mode is the default. Click or tap a cell to color it in as part of the picture; click or tap a filled cell again to clear it back to blank.
• Mark mode is for cells you've worked out must stay empty. Click or tap the Fill/Mark button to switch into it, then click or tap a cell to place or remove an X. Marks are a memory aid only; finishing the puzzle only checks the filled cells.
• Cross-referencing is the core skill. What you deduce in a row narrows the possibilities in the columns it crosses, and back again, until the whole grid resolves.

The puzzle is complete when every cell matches its clues, revealing the hidden picture.

The grids grow larger across eight levels, so the deductions get longer while the method stays exactly the same.

Tips

• Start with the biggest clues. A long run in a line has few places it can fit, so it forces some cells to be filled no matter what. Those guaranteed cells give you a foothold to build from.
• Look for lines that are completely full. If a row's clues plus the required gaps add up to the whole width, the entire line is determined at once, which is the fastest kind of progress.
• Mark empty cells, not just filled ones. Knowing a cell must be blank is as useful as knowing it is filled, since it splits a line into sections and rules out where blocks can go.
• Overlap long runs to find sure cells. Slide a long block to its leftmost and rightmost positions in a line. Any cells covered in both cases must be filled, even before you know exactly where the block sits.
• Switch between rows and columns often. Progress in one direction unlocks the other, so whenever a row stalls, look at the columns it feeds into, and keep bouncing back and forth.
• Never guess. Every cell can be deduced from the clues, so if you are tempted to guess, there is a logical step waiting to be found. Guessing usually leads to a contradiction later.

Frequently asked questions