Lesson 5 of 5
Solving techniques
4 min

Nonogram Joining and Splitting Techniques

The overlap and the edges place blocks from the ends of a line. Joining and splitting work from the inside, on cells you have already filled. This lesson uses a 10×10 picture: a mug of coffee.

Step 1 of 5

Join them
Row 9's clue is a single 5, and two of its cells are filled, in columns 3 and 6. A line with one block has only one run of filled cells, so both cells are in the 5, and so is everything between them. Join them: columns 4 and 5, starred, are filled.
Fill the gap
The block now covers columns 3 to 6, four of its five cells.
Your move
Join the two filled cells of row 9.
Split them
Row 2's clue is 2 2, and columns 5 and 7 are filled. Fill column 6 between them and you'd make a block of at least three, longer than any number in the clue. So column 6 is empty, and the two cells are in different blocks: split them. Then each 2 has only one way to go, away from the split.
Your move
Cross out the cell between the two filled cells, then complete both 2s.
Which block is which?
Joining needs to know that two cells share a block. Column 1's clue is 4 1, and rows 5, 8 and 10 are filled. Row 10 can't be in the 4: a 4 that reached row 10 would start in row 7 and miss row 5, and nothing comes before the 4. So row 10 is the 1, and rows 5 and 8 are both in the 4.
Your move
Join rows 5 and 8 in column 1.
Join or split?
Column 9's clue is 3 1, and its cells in rows 6 and 8 are filled. Is the starred cell between them, in row 7, filled?
Question

What you learned

Two filled cells in the same block: fill every cell between them.
If joining two filled cells would make a block longer than any number in the clue, the cell between them is empty.
Work out which block a filled cell belongs to before you join it to anything.