Currently I'm trying to implement Scrabble with MuZero.
The $15 \times 15$ game board observation (as input) is of size $27 \times15 \times15$ (26 letters + 1 wildcard) with a value of 0 or 1.
However I'm having difficulties finding a suitable way to encode the player's rack of letters (Always 7 letters on the rack).
The available tiles are: 26 letters $(A-Z)$ and 1 wildcard.
A rack can also contain multiple tiles of the same letter.
Example: rack of player 1 is $[A,A,C,E,T,T,H] -> A:2x, C:1x, E:1x, T:2x, H:1x$
How can I represent a rack of tiles as a $(? \times)15 \times15$ (or other board size) matrix ?