Last cell standing in a row

By the Queenwise team · Updated October 9, 2026

A row or column with no crown still needs exactly one. If all but one of its cells are ruled out, the remaining cell must hold a crown, whichever region contains it.

This rule is different from scanning a region. A cell can be forced by its row even when its colored region still has several candidates elsewhere.

• Check narrow candidate lists before scanning the whole board.
• A line that already contains a crown is finished; its other cells are excluded.
• After the forced placement, scan both its region and the crossing line for new singletons.

Why it works

Rows and columns follow the same counting rule as regions: each needs exactly one crown. When every cell but one in a row is ruled out, that cell is forced — even if its own region still has other options. The row decides for the region.

How to spot it fast

• After each crown, check the rows and columns that pass next to it: the touching ring removes up to three cells from each neighboring row.
• Scan edge rows and columns; they are often short of candidates because big regions fill them.
• On large boards, count candidates row by row instead of looking at the whole board at once.

Common mistakes

• Only scanning regions. Many forced crowns come from rows and columns, especially on 10×10 and larger boards.
• Forgetting finished lines. A row that already has a crown is done; every other cell in it is excluded.

Try it on a practice puzzle

How often this technique appears

Across all 4,000 levels, our logic engine needs this technique on the following share of boards at each size: