ABCD

You’re given an empty grid, and several rows of numbers on the side. You have to write a letter in every empty cell, following these rules:

  1. The numbers on the edge indicate how many instances of a specific letter appear in that row or column.
  2. Identical letters can not be horizontally or vertically adjacent.

The inventor of this type is unknown. This puzzle is also known under the names ABCD Puzzle, ABC-Kombi or ABCD-Rätsel.

More information: https://www.janko.at/Raetsel/Abc-Kombi/index.htm

Controls

ABCD uses the same control scheme as Solo, but with letters instead of numbers.

Left-click to select a cell, then type a letter on your keyboard to enter it. Press Backspace or Space to clear a cell.

Right-click a cell, then type a letter to add a pencil mark. Pencil marks can be used for any purpose. A preference makes right-click switch on a sticky pencil mode instead, which stays on until you right-click again.

You can also use the arrow keys to move the selected cell around. Press Enter to toggle between entering letters and entering pencil marks.

Press the ‘M’ key to fill every empty cell with all possible pencil marks.

ABCD parameters

These parameters are available from the ‘Custom…’ option on the ‘Type’ menu.

Width, Height
Size of the grid in squares (excluding the size of the numbers on the edge). How large a board can be depends on the number of letters, because each extra letter is another count every row and column has to satisfy: with three letters a board can reach about 130 squares, with four about 80, and from six letters up about 65. Long thin boards go much further — a short row is almost settled by its own numbers — so anything up to about 160 squares is allowed when one side is under 6. Past those limits no puzzle with a single solution is likely to exist at all, so the game says so rather than searching for one.
Letters
The amount of different letters that can appear in the puzzle.
Remove clues
When enabled, the difficulty is increased by hiding certain number clues.
Allow diagonal touching
When disabled, letters cannot be diagonally adjacent (in addition to letters not being orthogonally adjacent). Counter-intuitively this raises the size limit described above rather than lowering it: the extra restriction gives you more to reason from, so larger boards still work out to a single solution.

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