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latin_solver_alloc: handle clashing numbers in input grid.

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In the setup phase of the centralised latin.c solver, we start by
going over the input grid containing already-placed clue numbers, and
calling latin_solver_place to enter each on into the solver's data
structure. This has the side effect of ruling out each number from the
rest of the row and column, and _also_ checking by assertion that the
number being placed is not ruled out.

Those are a bad combination, because it means that if you give an
obviously inconsistent input grid to latin_solver_alloc (e.g. with two
identical numbers in a row already), it will fail an assertion. In
that situation, you want the solver run as a whole to return
diff_impossible so that the error is reported cleanly.

This assertion failure could be provoked by giving either Towers or
Group a manually-constructed game description inconsistent in that
way, and hitting Solve. Worse, it could be provoked during live play
in Unequal, by filling in a number clashing with a clue and then
pressing 'h' to get hints.
This commit is contained in:
Simon Tatham
2023-02-05 10:29:42 +00:00
parent 517b14e666
commit 5030d87903
4 changed files with 60 additions and 41 deletions
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15
unfinished/group.c
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@ -580,13 +580,11 @@ static int solver(const game_params *params, digit *grid, int maxdiff)
int w = params->w;
int ret;
struct latin_solver solver;
#ifdef STANDALONE_SOLVER
char *p, text[100], *names[50];
int i;
#endif
latin_solver_alloc(&solver, grid, w);
#ifdef STANDALONE_SOLVER
for (i = 0, p = text; i < w; i++) {
names[i] = p;
*p++ = TOCHAR(i+1, params->id);
@ -595,10 +593,13 @@ static int solver(const game_params *params, digit *grid, int maxdiff)
solver.names = names;
#endif
ret = latin_solver_main(&solver, maxdiff,
DIFF_TRIVIAL, DIFF_HARD, DIFF_EXTREME,
DIFF_EXTREME, DIFF_UNREASONABLE,
group_solvers, group_valid, NULL, NULL, NULL);
if (latin_solver_alloc(&solver, grid, w))
ret = latin_solver_main(&solver, maxdiff,
DIFF_TRIVIAL, DIFF_HARD, DIFF_EXTREME,
DIFF_EXTREME, DIFF_UNREASONABLE,
group_solvers, group_valid, NULL, NULL, NULL);
else
ret = diff_impossible;
latin_solver_free(&solver);