Speed up a slow loop

[Alex Tweedly]

Yes, Quentin's allowing for diagonals (that's how the number of digraphs 
on a 5x5 board gets up to 110).

And it's probably a good idea, allowing an even finer filter - if you 
aren't doing the boardwalk method..

If you do use the boardwalk to generate the exact list of words, you get 
no benefit from single-letter or digraph filtering, because the 
tree-walk is constrained to only those valid "next char"s, and so 
implicitly avoids using those non-present digraphs.

Oh - so many different ways to do things, all interesting, and all good 
for some variation of the problem.


btw - that reminds me - back when I used to play real, physical Boggle 
with friends, we often played variants of the word rules; either

  - you can reuse the same tile later in a word (e.g.
Y  L  A
X  E  T

would allow "lately" as a word.

OR

- you can double-up on a tile (e.g. M I L would allow 'mill')
(more important if you're British than if you're American :-)

Alex.