A finished line is a row or column whose filled squares already match its clue. Every other square in it must be empty, so cross them all out. It’s the simplest technique, and after the overlap it’s the one you’ll use most: every puzzle needs it, many times.
This is the first of the Nonogram techniques.
The rule
- Check whether a line’s filled squares form exactly the runs in its clue, in order.
- If they do, cross out every square in the line that isn’t filled.
In a real puzzle
Every technique page follows the same 10×10 from the game. Finished lines first come up at step 10: row 6 needs 2 4, and squares 1 and 2 and squares 4 to 7 are already filled. That’s a 2 and a 4, so the line is done.
Those four crosses matter to the columns they sit in. A crossed-out square in row 6 is one the blocks of columns 3, 8, 9 and 10 can’t use. The puzzle uses this technique 17 times in its 49 steps.
Why it matters so much
On its own, a finished line tells you nothing new about itself. Its value is in the crosses it gives the crossing lines, which is why leaving empty squares uncrossed is one of the costliest mistakes: we found that a solver that never records crosses can’t finish a single 10×10 or 15×15.