Tapa is a puzzle created by Serkan Yurekli; I believe it was first unveiled in the OAPC competitions of 2009. The object is to determine whether each grid cell is filled in or not. Grid cells must be filled in so that all the black cells form one contiguous region, not counting squares touching at a corner to be adjacent, but it is not allowed to have a two by two square of black cells. Clue cells with numbers may not be filled in and tell the length of each consecutive black cell block in the eight surrounding cells. Two cell blocks clued by two different numbers must be separated by at least one white cell.
Below is an example puzzle and its only solution.
- Some clues will feature question marks. Each question mark can represent any nonzero integer. You must deduce what it is yourself.