How to Play Nonocross

The rules in 30 seconds

• Each number beside a row or above a column is a group of filled cells in a straight line.
• Several numbers mean several groups, in the same order as written: left to right for rows, top to bottom for columns.
• Groups in the same line are separated by at least one empty cell.
• A line with the clue 0 stays empty.
• When every row and column matches its numbers, the picture is complete.

How to read a clue

Take a row of 10 cells with the clue 3 2. It means: somewhere in this row there is a group of 3 filled cells, then at least one empty cell, then a group of 2. It does not tell you where the groups start. Before the first group and after the last there can be any number of empty cells, including none.

The quickest check is the minimum length: add the numbers and one gap between each pair. For 3 2 that is 3 + 1 + 2 = 6 cells. In a row of 10 that leaves 4 spare cells, and the fewer spare cells a line has, the more of it you can fill straight away.

Technique 1: Full lines

If the minimum length equals the line length, there is only one way to place the groups. A clue of 6 in a 6-cell row fills every cell. A clue of 2 3 in a 6-cell row fills cells 1 and 2 and cells 4 to 6, with cell 3 crossed out, because 2 + 1 + 3 = 6.

Look for these first in every level. In Level 14 (Umbrella), four of its ten lines are full lines.

Technique 2: The overlap

When a group is bigger than half its line, some of its cells are filled no matter where it sits. Slide the group as far left as it can go, then as far right. The cells it covers both times must be filled.

Example: a clue of 6 in an 8-cell row. Pushed left it covers cells 1 to 6, pushed right cells 3 to 8. Cells 3 to 6 are covered both times, so fill them. Quick rule: the number of sure cells is the clue minus the spare cells, here 6 - 2 = 4.

The same works with several groups: push all of them left, then all of them right, and compare each group with itself.

Technique 3: Empty and finished lines

A line with the clue 0 is empty, so cross out every cell. And as soon as a line has all its groups in place, every other cell in it is empty too. Example: a 6-cell row with the clue 2 where cells 3 and 4 are already filled. The group is complete, so cells 1, 2, 5 and 6 get crosses.

Finished lines are easy to skip, and crossing them out is often the move that unlocks the lines that cross them.

Technique 4: Start from the edges

A filled cell at the very start of a line must belong to the first group, so the whole first group starts there. Example: a 7-cell row with the clue 3 1 and cell 1 filled. The 3 must cover cells 1 to 3, and cell 4 must be empty to separate it from the 1.

The same works backwards from the last cell with the last group. A crossed cell near the edge helps too: if the space before it is too short for the first group, cross that space out as well.

Technique 5: Cross-check every cell

Every cell sits in one row and one column. When you fill or cross a cell while working on a row, the column through it has changed, so read that column again. In medium and hard levels most progress comes from this back and forth, not from any single line.

A simple routine: after each move, check the line that crosses the cell you just changed. If nothing new follows, move to the line with the fewest spare cells.

Worked example: Level 14 (Umbrella)

Level 14 is a 5x5 grid. Row clues from top to bottom: 3, 5, 5, 1, 2. Column clues from left to right: 2, 3, 5, 3 1, 2.

1. Full lines. Rows 2 and 3 have the clue 5, so fill them completely. Column 3 has the clue 5: fill it. Column 4 has 3 1, and 3 + 1 + 1 = 5, so it is a full line too: fill cells 1 to 3, cross cell 4, fill cell 5.

2. Finished lines. Column 1 and column 5 both have the clue 2, and both now have their two filled cells in rows 2 and 3. They are complete, so cross out rows 1, 4 and 5 in both columns.

3. Row 1, clue 3. Cells 1 and 5 are crossed, which leaves cells 2 to 4 for a group of 3. Fill cell 2; cells 3 and 4 are already filled.

4. Column 2, clue 3. Rows 1 to 3 are filled, so the group is complete. Cross out rows 4 and 5.

5. Check every line. Row 4 has one filled cell and Row 5 has two, matching their clues, and every column matches too. The umbrella is finished.

Four moves and a check, three techniques, no guessing. Open Level 14 to try it on the play grid.

Fill or cross: use both marks

Mark every cell you know is empty with a cross. On our play grid a cross is not part of the answer, but it stops you from filling that cell by mistake and it shortens the space the next group has to fit in. Tap once to fill, twice to cross, three times to clear.

When you are stuck

• Go through every line once more and look for one you can finish with crosses. Finished lines are easy to miss.
• Find the line with the fewest spare cells and apply the overlap.
• Check both ends of every line for filled cells touching the border.
• Still nothing? Press Hint on the level page. It fills one cell based on your own board and names the technique, so you can carry on yourself.
• On the eight levels with more than one solution, logic runs out before the grid is full. Use the picture to decide the last cells.

Practice levels

Try each technique on a real grid:

• Full lines: Level 5 (Chick), 5x5. Three of its rows are full lines.
• Overlap: Level 7 (Cake), 5x5. The 3 in row 3 and the 3s in columns 2 and 4 each give you a sure middle cell.
• Finished lines: Level 14 (Umbrella), 5x5, as in the example above.
• Edges: Level 6 (Pig), 5x5. Once the full outer columns are in, every row starts and ends at the border.
• Everything together: Level 33 (Turtle), the first 10x10 grid.

Nonocross rules: quick answers

Ready to solve? Pick your level from all 60 Nonocross answers.