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Dominosa: be more careful about >= Hard layout.

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Now we don't just ensure that alloc_try_hard arranged a confounder for
every domino; we also make sure that the full Basic-mode solver can't
place even a single domino with certainty.
This commit is contained in:
Simon Tatham
2019-04-11 19:39:03 +01:00
parent 59ac8a69af
commit 1e6e3a815e
1 changed files with 37 additions and 1 deletions
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38
dominosa.c
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@ -1916,9 +1916,45 @@ static char *new_game_desc(const game_params *params, random_state *rs,
if (!alloc_try_unique(as, rs))
continue;
} else {
/* Try to arrange that there is no easy starting point */
/*
* For Hard puzzles and above, we'd like there not to be
* any easy toehold to start with.
*
* Mostly, that's arranged by alloc_try_hard, which will
* ensure that no domino starts off with only one
* potential placement. But a few other deductions
* possible at Basic level can still sneak through the
* cracks - for example, if the only two placements of one
* domino overlap in a square, and you therefore rule out
* some other domino that can use that square, you might
* then find that _that_ domino now has only one
* placement, and you've made a start.
*
* Of course, the main difficulty-level check will still
* guarantee that you have to do a harder deduction
* _somewhere_ in the grid. But it's more elegant if
* there's nowhere obvious to get started at all.
*/
int di;
bool ok;
if (!alloc_try_hard(as, rs))
continue;
solver_setup_grid(sc, as->numbers);
if (run_solver(sc, DIFF_BASIC) < 2)
continue;
ok = true;
for (di = 0; di < sc->dc; di++)
if (sc->dominoes[di].nplacements <= 1) {
ok = false;
break;
}
if (!ok) {
continue;
}
}
if (diff != DIFF_AMBIGUOUS) {