Every square holds a black stone or a white stone. A few are given. All the black stones must join up into a single group, moving across or down from stone to stone — and the white stones must too.
Two small rules keep the groups honest. No 2×2 block may be all one colour, so the groups stay thin and winding. And no 2×2 block may be a checkerboard, because two blacks touching only at a corner would cut the whites apart (and the other way round).
The result is two interlocking shapes, like the yin and yang symbol — every puzzle has exactly one answer.
Fill every square black or white so that each colour forms one connected group, with no solid or checkerboard 2×2.
The full guide, with a worked example and common mistakes: How to play Yin and Yang.
No — stones join only across or down.
In a 2×2 checkerboard, each colour touches only at a corner, so one of the two colours would be split.
Yes — every puzzle is checked so that logic alone reaches the unique answer.