Aapo Rantalainen points out that comparing 'char c' against zero gives
rise to gcc's "comparison is always false" warning, which escalates to
an error under -Werror.
This is one of those situations where the warning is doing more harm
than good, but here's a rephrasing which casts to unsigned so that
both negative numbers and positive out-of-range ones can be caught by
the same comparison.
Previously it simply chose every move based on the static evaluation
function 'minimise the pair (longest shortest-path to any square,
number of squares at that distance)'. Now it looks three moves ahead
recursively, and I've also adjusted the evaluation function to tie-
break based on the number of squares brought to distance zero (i.e.
actually in control).
The result isn't an unconditional improvement on the old solver; in a
test run based on 'flood --generate 1000 12x12c6m0#12345' I found that
57 out of 1000 grids tested now had longer solutions. However, about
three quarters had shorter ones, and solutions are more than a move
shorter on average.
The ones I started with were a bit under-varied and over-orthogonal.
Get rid of some of the more pointless things like 16x16 with lots of
extra moves, and add some with different colour counts. While I'm
here, make the menu descriptions nicer.
Based on a web game I saw a few years ago, and dashed off this weekend
after I thought of a way to write a good (though not quite optimal)
heuristic solver, here's a random little thing not quite in the same
line as the most usual kind of Puzzles fare: instead of making you
scratch your head to find any move to make at all, it's easy to find
solutions in principle, and the challenge comes from having to do so
within a move limit.
