Tapa

Tapa Example

Tapa is a puzzle genre. Unfortunately the origin of Tapa is unknown to me as of the time of update.

Cell types

In an unsolved puzzle, there seem to be only two cell types, unknown cells (white cells) and given cells. However, the task in Tapa is to shade some unknown cells to form shaded cells, while leaving other unknown cells unshaded.

Due to technical limitations, the digits of a clue cannot be separated further. Just remember that every clue must be single-digit, since there are only at most eight surrounding cells of any cell.

Interaction

Each given tells the number of continuous shaded cells around it. For example, a “7” clue tells that there are 7 shaded cells around the given cell, all in a continuous group, while a “1 1” clue tells that there is one shaded cell, continued with some (at least one) unshaded cells, then continued with another one shaded cell, continued with some more (at least one) unshaded cells. A “?” can stand for any digit other than 0.

The shaded cells, as most shading-cells-type puzzles like Nurikabe, must form a contiguous region, without any 2×2 square of shaded cells.

Objective

Shade some cells to satisfy all the givens and all the above conditions.

Walkthrough of the example

First, start with the “1 1”. The only way to complete this given is to put shaded cells at R1C3 and R2C4, leaving R2C3 blank.

Since R2C3 is blank, there are exactly seven cells remaining around the 7, so all seven cells are shaded.

Since the black cells form a contiguous region, R1C2 and R3C4 must be shaded, otherwise R1C3 or R2C4, respectively, will be isolated.

Now, since there may not be any 2×2 square of shaded cells, R4C4 can’t be shaded, and everything is complete.