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Dominosa: move set analysis with doubles into Extreme.

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This change doesn't alter the overall power of the Dominosa solver; it
just moves the boundary between Hard and Extreme so that fewer puzzles
count as Hard, and more as Extreme. Specifically, either of the two
cases of set analysis potentially involving a double domino with both
squares in the set is now classed as Extreme.

The effects on difficulty are that Hard is now easier, and Extreme is
at least easier _on average_. But the main purpose is the effect on
generation time: before this change, Dominosa Extreme was the slowest
puzzle present to generate in the whole collection, by a factor of
more than three. I think the forcing-chain deductions just didn't make
very many additional grids soluble, so that the generator had to try a
lot of candidates before finding one that could be solved using
forcing chains but not with all the other techniques put together.
This commit is contained in:
Simon Tatham
2019-04-13 15:57:28 +01:00
parent 9f0dfba5fa
commit 1ffc737130
1 changed files with 12 additions and 2 deletions
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14
dominosa.c
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@ -1013,7 +1013,7 @@ static bool deduce_parity(struct solver_scratch *sc)
* is small enough to let us rule out placements of those dominoes
* elsewhere.
*/
static bool deduce_set_simple(struct solver_scratch *sc)
static bool deduce_set(struct solver_scratch *sc, bool doubles)
{
struct solver_square **sqs, **sqp, **sqe;
int num, nsq, i, j;
@ -1195,6 +1195,9 @@ static bool deduce_set_simple(struct solver_scratch *sc)
rule_out_text = "all of them elsewhere";
#endif
} else {
if (!doubles)
continue; /* not at this difficulty level */
/*
* But in Dominosa, there's a special case if _two_
* squares in this set can possibly both be covered by
@ -1761,7 +1764,7 @@ static int run_solver(struct solver_scratch *sc, int max_diff_allowed)
if (max_diff_allowed <= DIFF_BASIC)
continue;
if (deduce_set_simple(sc))
if (deduce_set(sc, false))
done_something = true;
if (done_something) {
sc->max_diff_used = max(sc->max_diff_used, DIFF_HARD);
@ -1771,6 +1774,13 @@ static int run_solver(struct solver_scratch *sc, int max_diff_allowed)
if (max_diff_allowed <= DIFF_HARD)
continue;
if (deduce_set(sc, true))
done_something = true;
if (done_something) {
sc->max_diff_used = max(sc->max_diff_used, DIFF_EXTREME);
continue;
}
if (deduce_forcing_chain(sc))
done_something = true;
if (done_something) {