When a region claims a whole row

By the Queenwise team · Updated October 9, 2026

Suppose all remaining candidates of region B are in row 3. B must place its crown somewhere in that row. Because row 3 permits only one crown, every candidate in row 3 outside B is ruled out.

You have not learned which cell in B holds the crown. Do not place it arbitrarily. The deduction is an elimination in other regions, and that elimination may create a forced placement elsewhere.

• List every surviving candidate in the region, not just two cells that caught your eye.
• Check whether all candidates share a row or a column.
• Cross out other regions' candidates on that line, then rescan for singletons.

Why it works

If all of a region's remaining cells lie in one row, the region's crown will be in that row — we just do not know which cell yet. Since the row can hold only one crown, it cannot take a crown from any other region, so every other region's cells in that row are eliminated. The same holds for columns.

This line lock is the most important technique after forced crowns: our logic engine needs it on nearly every board, and it is what turns medium puzzles into easy ones once you see it.

How to spot it fast

• Look for long, thin regions that lie flat along one row or stand upright in one column.
• Re-check regions that just lost cells: an L-shaped region often collapses into a single line after one crown.
• Mark the eliminations immediately, then look for new forced crowns in the regions you trimmed.

Common mistakes

• Placing a crown in the locked region. The lock tells you the row, not the cell.
• Missing one stray candidate. If a single candidate of the region sits outside the line, there is no lock.

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: