The one-spot region

By the Queenwise team · Updated October 9, 2026

Every colored region needs exactly one crown. If only one candidate remains in a region without a crown, place its crown there. The region can be large or small; the number of remaining candidates matters.

A candidate is a cell that does not share a row, column or region with a placed crown and does not touch one. A proved elimination can remove an additional candidate. An X you placed without proof is a note, so check its reason before treating a region as a singleton.

• Count candidates only in regions that still need a crown.
• After each placement or proved elimination, scan affected regions again.
• If no candidate survives, audit your earlier move or notes. Zero candidates is a contradiction, not a forced placement.

Why it works

Every region must hold exactly one crown, and a crown can only stand on a legal cell. If a region has exactly one legal cell left, the region's crown has nowhere else to go. This is the most common deduction in the game: our logic engine uses it on every single board, at every size.

How to spot it fast

• Start with the smallest regions. A three-cell region needs only two eliminations to become forced.
• Look at regions squeezed against a placed crown: one crown often wipes out most of a neighboring region through its row, column and touching ring.
• Re-check a region every time a crown lands in the same row, column or next to it.

Common mistakes

• Counting marks you are not sure about. Only proved eliminations count; a hopeful X can hide the real last cell.
• Ignoring large regions. A big region can still be down to one legal cell late in the puzzle.
• Placing a crown because a region has two cells left. Two candidates is not a forced move — look for a line lock instead.

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: