Nonogram Strategies: Overlap, Full Lines & Empty Squares

The most useful nonogram strategies identify squares that have the same state in every valid arrangement of a line. You do not need to know an entire row to make progress: a single guaranteed square can unlock a column, which can unlock another row.

1. Look for exact-fit lines

Add the clue numbers, then add the minimum separators. In a ten-square line with clues 3 2 3, the groups use eight squares and the two separators use the remaining two. There is only one arrangement:

This works for any line where the minimum required space equals its length. Mark the filled groups and separators, then immediately examine the crossing lines.

2. Find the overlap

Imagine placing a group as far left as possible, then as far right as possible. Any square filled in both extreme positions must be filled. For one group of 4 in a six-square line:

The two middle squares are certain. For a single group, the overlap length is twice the group length minus the available line length, when that result is positive. For multiple groups, include the space required by all neighboring groups and separators before applying the same reasoning.

Overlap with multiple numbers: a worked example

Take a blank seven-square line with clues 3 2. The groups need five filled squares and at least one separator, leaving one spare square. There are exactly three legal arrangements:

Squares 2, 3 and 6 are filled in every case, so fill those now. A question mark means unknown, not empty. None of the other four squares is initially a guaranteed ×. The × marks in each case describe that possible arrangement only.

If a crossing column later proves square 4 empty, Case C no longer fits. Cases A and B remain, so square 1 becomes certain as well. You still cannot decide squares 5 and 7 without more information. This is how a row and its crossing columns narrow one another down.

Compare the same group, not just the same square

With several clues, an apparent overlap can belong to different groups. In a five-square line with clues 1 1, the far-left layout is ■ × ■ × × and the far-right layout is × × ■ × ■. Both fill square 3, but it is the second group in the first layout and the first group in the second. The legal layout × ■ × ■ × leaves square 3 empty. Comparing those two pictures alone would give a false move.

For each clue, compare that same group's leftmost and rightmost legal positions, respecting all other clues and known marks. If there is no shared square, leave it undecided and inspect a crossing line. For the basic reading order and separators, return to the beginner rules; for paper practice, try our free nonogram worksheets.

3. Close completed groups

If a group already has its required length and you know it cannot belong to a longer clue, the squares immediately before and after it must be empty. A confirmed run of three for a lone clue 3 cannot grow into four. Marking those boundaries prevents accidental overfilling and narrows the crossing columns.

Be careful with repeated or different-sized clues. A run of two in a line with clues 2 4 may still be part of the group of four. First establish which clue the run belongs to.

4. Use empty squares to split the work

A confirmed empty square breaks a line into sections. Some groups may no longer fit in a section. If a clue of 4 cannot fit in a three-square section, it must belong elsewhere. But do not assign groups to sections too early: a section may contain zero groups, one group, or several smaller groups with separators.

5. Return to both directions

After each useful move, read the crossing row or column again. A square that seems unhelpful in one direction may establish the edge of a group in the other. A reliable rhythm is: find a certain square, inspect the crossing line, mark any confirmed separators, then scan the remaining lines.

When you get stuck

• Check the order of the clue groups.
• Confirm that you left at least one empty square between separate groups.
• Look for a long clue whose possible positions overlap.
• Check whether a completed run needs an empty boundary.
• Use Check to find conflicting marks before asking for a hint.

On Little Nonograms, a hint reveals one square rather than completing the whole grid. You can use that new information to resume deduction. A 5×5 Mini puzzle is a good place to practice these techniques before taking on a 10×10 Classic.