On 01/07/95 at 19:43:27 mreid@ptc.com said:

each configuration is stored with 2 bits of memory and thus the whole
space consumes about 42 megabytes. each configuration is assigned
one of 4 values:

distance is currently unknown
distance = current search depth
distance = current search depth - 1
distance < current search depth - 1

This little table reminded me of something I had meant to say about
storing the whole cube space in about 10^18 cells. In principle,
under the Q turn metric it would be possible for each cell to contain
only one bit by storing (depth mod 4)/2. However, in *building*
the solution I think you would need a value in the cell meaning
essentially "distance is currently unknown". Hence, you would need
at least three separate values and therefore at least two bits.
After the table were complete, it might be possible to reduce the
two bits down to one. Even then, you might want to be able to
identify those small percentage of cells which were empty, in which
case you would need two bits anyway. Under the Q+H metric, you
would need two bits in any case to store (depth mod 3), and the
fourth bit pattern would be available to represent "distance is
currently unknown" or "empty cell" as appropriate.

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