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Nonogram Line Solving: List Every Arrangement

Every arrangement is the slow, sure technique: list every way a line’s blocks can still fit, given what you already know, and settle any square that’s the same in all of them. It finds everything a single line can tell you. You only need it when the five quick techniques have nothing left anywhere on the grid.

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This is the last of the Nonogram techniques.

The rule

  1. Pick a line with few unknown squares.
  2. Write out every way its blocks could sit: in order, one gap apart, never on a crossed-out square, covering every filled square.
  3. Fill any square filled in all of them, and cross out any square empty in all of them.

In a real puzzle

In the 10×10 every technique page follows, the quick techniques run out at step 41: none of them finds anything on any line. Row 1 needs a single 2. Squares 1 to 3 and 6 to 8 are crossed out, and square 5 is filled.

The quick rules don’t see what to do, because packing ignores filled squares: packed right, the 2 could sit in squares 9 and 10. But the 2 is the only block, so it must cover square 5. With square 6 crossed out, it can only be squares 4 and 5. There’s just one arrangement left.

row 1, before and after row 1 with the clue 2, before and after this step. 2 2 before after
Row 1: the 2 must cover square 5 and can’t use square 6, so it’s squares 4 and 5. Squares 9 and 10 are crossed out.
every arrangement in the 10 by 10 puzzle The puzzle at step 41 of 49, just after this technique settles row 1 (clue 2). The squares it settled are highlighted. 2 1 3 2 6 2 1 2 2 3 1 2 4 9 5 3 2 3 3 6 6 1 4 1 6 3 5 5 2 2 1 2 1 2 3 1 2 3
The puzzle at step 41, with row 1 highlighted.

That’s the only time this puzzle needs it. The remaining eight steps are quick ones.

The 10 by 10 puzzle, solved The finished picture, after 49 steps. 2 1 3 2 6 2 1 2 2 3 1 2 4 9 5 3 2 3 3 6 6 1 4 1 6 3 5 5 2 2 1 2 1 2 3 1 2 3
The finished puzzle, after 49 steps.

A bigger example

The how-to-solve walkthrough has a line with three arrangements left, where the filled pair has to be the 2 of a 1 2 clue. Listing them shows three squares that are empty in all of them.

How often you’ll need it

On 100 of the game’s puzzles per size, every arrangement was needed in 7 of the 5×5s, 22 of the 10×10s and 70 of the 15×15s. On a big puzzle it’s a normal part of the solve: the average 15×15 needs it about six times.

Next steps

Questions

Isn't listing arrangements just guessing?

No. Guessing picks one arrangement and hopes. Listing them all and keeping only what they agree on is certain: every square it settles is right however the rest turns out.

Which line should I list?

One with few unknown squares, or with filled squares whose block you can’t place. The fewer ways the line has left, the quicker it is to list them.

How often will I need it?

On the game’s 5×5s, rarely: 7 puzzles in 100. On 15×15s, 70 in 100, about six times per puzzle on average.