chiark / gitweb /
Range: add pencil marks to squares by Shift-cursor keys.
[sgt-puzzles.git] / unequal.c
index 3761b629a801272ff054f493c5dc49144dea6c49..54300e1288609819dcd3ef2cae604caf0a175a43 100644 (file)
--- a/unequal.c
+++ b/unequal.c
@@ -87,21 +87,20 @@ struct game_state {
  */
 
 /* Steal the method from map.c for difficulty levels. */
-#define DIFFLIST(A)             \
-    A(LATIN,Trivial,t)          \
-    A(EASY,Easy,e)              \
-    A(SET,Tricky,k)             \
-    A(EXTREME,Extreme,x)        \
-    A(RECURSIVE,Recursive,r)
-
-#define ENUM(upper,title,lower) DIFF_ ## upper,
-#define TITLE(upper,title,lower) #title,
-#define ENCODE(upper,title,lower) #lower
-#define CONFIG(upper,title,lower) ":" #title
-enum { DIFFLIST(ENUM) DIFF_IMPOSSIBLE = diff_impossible, DIFF_AMBIGUOUS = diff_ambiguous, DIFF_UNFINISHED = diff_unfinished };
+#define DIFFLIST(A)               \
+    A(LATIN,Trivial,NULL,t)       \
+    A(EASY,Easy,solver_easy, e)   \
+    A(SET,Tricky,solver_set, k)   \
+    A(EXTREME,Extreme,NULL,x)     \
+    A(RECURSIVE,Recursive,NULL,r)
+
+#define ENUM(upper,title,func,lower) DIFF_ ## upper,
+#define TITLE(upper,title,func,lower) #title,
+#define ENCODE(upper,title,func,lower) #lower
+#define CONFIG(upper,title,func,lower) ":" #title
+enum { DIFFLIST(ENUM) DIFFCOUNT, DIFF_IMPOSSIBLE = diff_impossible, DIFF_AMBIGUOUS = diff_ambiguous, DIFF_UNFINISHED = diff_unfinished };
 static char const *const unequal_diffnames[] = { DIFFLIST(TITLE) };
 static char const unequal_diffchars[] = DIFFLIST(ENCODE);
-#define DIFFCOUNT lenof(unequal_diffchars)
 #define DIFFCONFIG DIFFLIST(CONFIG)
 
 #define DEFAULT_PRESET 0
@@ -157,7 +156,7 @@ static void free_params(game_params *params)
     sfree(params);
 }
 
-static game_params *dup_params(game_params *params)
+static game_params *dup_params(const game_params *params)
 {
     game_params *ret = snew(game_params);
     *ret = *params;       /* structure copy */
@@ -191,7 +190,7 @@ static void decode_params(game_params *ret, char const *string)
     }
 }
 
-static char *encode_params(game_params *params, int full)
+static char *encode_params(const game_params *params, int full)
 {
     char ret[80];
 
@@ -204,7 +203,7 @@ static char *encode_params(game_params *params, int full)
     return dupstr(ret);
 }
 
-static config_item *game_configure(game_params *params)
+static config_item *game_configure(const game_params *params)
 {
     config_item *ret;
     char buf[80];
@@ -235,7 +234,7 @@ static config_item *game_configure(game_params *params)
     return ret;
 }
 
-static game_params *custom_params(config_item *cfg)
+static game_params *custom_params(const config_item *cfg)
 {
     game_params *ret = snew(game_params);
 
@@ -246,7 +245,7 @@ static game_params *custom_params(config_item *cfg)
     return ret;
 }
 
-static char *validate_params(game_params *params, int full)
+static char *validate_params(const game_params *params, int full)
 {
     if (params->order < 3 || params->order > 32)
         return "Order must be between 3 and 32";
@@ -289,7 +288,7 @@ static game_state *blank_game(int order, int adjacent)
     return state;
 }
 
-static game_state *dup_game(game_state *state)
+static game_state *dup_game(const game_state *state)
 {
     game_state *ret = blank_game(state->order, state->adjacent);
     int o2 = state->order*state->order, o3 = o2*state->order;
@@ -447,12 +446,12 @@ static int c2n(int c, int order) {
     return -1;
 }
 
-static int game_can_format_as_text_now(game_params *params)
+static int game_can_format_as_text_now(const game_params *params)
 {
     return TRUE;
 }
 
-static char *game_text_format(game_state *state)
+static char *game_text_format(const game_state *state)
 {
     int x, y, len, n;
     char *ret, *p;
@@ -523,88 +522,75 @@ struct solver_link {
     int len, gx, gy, lx, ly;
 };
 
-typedef struct game_solver {
-    struct latin_solver latin; /* keep first in struct! */
-
+struct solver_ctx {
     game_state *state;
 
     int nlinks, alinks;
     struct solver_link *links;
-} game_solver;
-
-#if 0
-static void solver_debug(game_solver *solver, int wide)
-{
-#ifdef STANDALONE_SOLVER
-    if (solver_show_working) {
-        if (!wide)
-            game_debug(solver->state);
-        else
-            latin_solver_debug(solver->latin.cube, solver->latin.o);
-    }
-#endif
-}
-#endif
+};
 
-static void solver_add_link(game_solver *solver,
+static void solver_add_link(struct solver_ctx *ctx,
                             int gx, int gy, int lx, int ly, int len)
 {
-    if (solver->alinks < solver->nlinks+1) {
-        solver->alinks = solver->alinks*2 + 1;
-        /*debug(("resizing solver->links, new size %d", solver->alinks));*/
-        solver->links = sresize(solver->links, solver->alinks, struct solver_link);
+    if (ctx->alinks < ctx->nlinks+1) {
+        ctx->alinks = ctx->alinks*2 + 1;
+        /*debug(("resizing ctx->links, new size %d", ctx->alinks));*/
+        ctx->links = sresize(ctx->links, ctx->alinks, struct solver_link);
     }
-    solver->links[solver->nlinks].gx = gx;
-    solver->links[solver->nlinks].gy = gy;
-    solver->links[solver->nlinks].lx = lx;
-    solver->links[solver->nlinks].ly = ly;
-    solver->links[solver->nlinks].len = len;
-    solver->nlinks++;
+    ctx->links[ctx->nlinks].gx = gx;
+    ctx->links[ctx->nlinks].gy = gy;
+    ctx->links[ctx->nlinks].lx = lx;
+    ctx->links[ctx->nlinks].ly = ly;
+    ctx->links[ctx->nlinks].len = len;
+    ctx->nlinks++;
     /*debug(("Adding new link: len %d (%d,%d) < (%d,%d), nlinks now %d",
-           len, lx, ly, gx, gy, solver->nlinks));*/
+           len, lx, ly, gx, gy, ctx->nlinks));*/
 }
 
-static game_solver *new_solver(digit *grid, game_state *state)
+static struct solver_ctx *new_ctx(game_state *state)
 {
-    game_solver *solver = snew(game_solver);
+    struct solver_ctx *ctx = snew(struct solver_ctx);
     int o = state->order;
     int i, x, y;
     unsigned int f;
 
-    latin_solver_alloc(&solver->latin, grid, o);
-
-    solver->nlinks = solver->alinks = 0;
-    solver->links = NULL;
-    solver->state = state;
+    ctx->nlinks = ctx->alinks = 0;
+    ctx->links = NULL;
+    ctx->state = state;
 
-    if (state->adjacent) return solver; /* adjacent mode doesn't use links. */
+    if (state->adjacent) return ctx; /* adjacent mode doesn't use links. */
 
     for (x = 0; x < o; x++) {
         for (y = 0; y < o; y++) {
             f = GRID(state, flags, x, y);
             for (i = 0; i < 4; i++) {
                 if (f & adjthan[i].f)
-                    solver_add_link(solver, x, y, x+adjthan[i].dx, y+adjthan[i].dy, 1);
+                    solver_add_link(ctx, x, y, x+adjthan[i].dx, y+adjthan[i].dy, 1);
             }
         }
     }
 
-    return solver;
+    return ctx;
+}
+
+static void *clone_ctx(void *vctx)
+{
+    struct solver_ctx *ctx = (struct solver_ctx *)vctx;
+    return new_ctx(ctx->state);
 }
 
-static void free_solver(game_solver *solver)
+static void free_ctx(void *vctx)
 {
-    if (solver->links) sfree(solver->links);
-    latin_solver_free(&solver->latin);
-    sfree(solver);
+    struct solver_ctx *ctx = (struct solver_ctx *)vctx;
+    if (ctx->links) sfree(ctx->links);
+    sfree(ctx);
 }
 
-static void solver_nminmax(game_solver *usolver,
+static void solver_nminmax(struct latin_solver *solver,
                            int x, int y, int *min_r, int *max_r,
                            unsigned char **ns_r)
 {
-    struct latin_solver *solver = &usolver->latin;
-    int o = usolver->latin.o, min = o, max = 0, n;
+    int o = solver->o, min = o, max = 0, n;
     unsigned char *ns;
 
     assert(x >= 0 && y >= 0 && x < o && y < o);
@@ -626,17 +612,17 @@ static void solver_nminmax(game_solver *usolver,
     if (ns_r) *ns_r = ns;
 }
 
-static int solver_links(game_solver *usolver)
+static int solver_links(struct latin_solver *solver, void *vctx)
 {
+    struct solver_ctx *ctx = (struct solver_ctx *)vctx;
     int i, j, lmin, gmax, nchanged = 0;
     unsigned char *gns, *lns;
     struct solver_link *link;
-    struct latin_solver *solver = &usolver->latin;
 
-    for (i = 0; i < usolver->nlinks; i++) {
-        link = &usolver->links[i];
-        solver_nminmax(usolver, link->gx, link->gy, NULL, &gmax, &gns);
-        solver_nminmax(usolver, link->lx, link->ly, &lmin, NULL, &lns);
+    for (i = 0; i < ctx->nlinks; i++) {
+        link = &ctx->links[i];
+        solver_nminmax(solver, link->gx, link->gy, NULL, &gmax, &gns);
+        solver_nminmax(solver, link->lx, link->ly, &lmin, NULL, &lns);
 
         for (j = 0; j < solver->o; j++) {
             /* For the 'greater' end of the link, discount all numbers
@@ -647,10 +633,10 @@ static int solver_links(game_solver *usolver)
                     if (solver_show_working) {
                         printf("%*slink elimination, (%d,%d) > (%d,%d):\n",
                                solver_recurse_depth*4, "",
-                               link->gx, link->gy, link->lx, link->ly);
+                               link->gx+1, link->gy+1, link->lx+1, link->ly+1);
                         printf("%*s  ruling out %d at (%d,%d)\n",
                                solver_recurse_depth*4, "",
-                               j+1, link->gx, link->gy);
+                               j+1, link->gx+1, link->gy+1);
                     }
 #endif
                     cube(link->gx, link->gy, j+1) = FALSE;
@@ -665,10 +651,10 @@ static int solver_links(game_solver *usolver)
                     if (solver_show_working) {
                         printf("%*slink elimination, (%d,%d) > (%d,%d):\n",
                                solver_recurse_depth*4, "",
-                               link->gx, link->gy, link->lx, link->ly);
+                               link->gx+1, link->gy+1, link->lx+1, link->ly+1);
                         printf("%*s  ruling out %d at (%d,%d)\n",
                                solver_recurse_depth*4, "",
-                               j+1, link->lx, link->ly);
+                               j+1, link->lx+1, link->ly+1);
                     }
 #endif
                     cube(link->lx, link->ly, j+1) = FALSE;
@@ -680,10 +666,10 @@ static int solver_links(game_solver *usolver)
     return nchanged;
 }
 
-static int solver_adjacent(game_solver *usolver)
+static int solver_adjacent(struct latin_solver *solver, void *vctx)
 {
-    struct latin_solver *solver = &usolver->latin;
-    int nchanged = 0, x, y, i, n, o = usolver->latin.o, nx, ny, gd;
+    struct solver_ctx *ctx = (struct solver_ctx *)vctx;
+    int nchanged = 0, x, y, i, n, o = solver->o, nx, ny, gd;
 
     /* Update possible values based on known values and adjacency clues. */
 
@@ -695,7 +681,7 @@ static int solver_adjacent(game_solver *usolver)
              * adjacent possibles reflect the adjacent/non-adjacent clue. */
 
             for (i = 0; i < 4; i++) {
-                int isadjacent = (GRID(usolver->state, flags, x, y) & adjthan[i].f);
+                int isadjacent = (GRID(ctx->state, flags, x, y) & adjthan[i].f);
 
                 nx = x + adjthan[i].dx, ny = y + adjthan[i].dy;
                 if (nx < 0 || ny < 0 || nx >= o || ny >= o)
@@ -715,9 +701,9 @@ static int solver_adjacent(game_solver *usolver)
                     if (solver_show_working) {
                         printf("%*sadjacent elimination, (%d,%d):%d %s (%d,%d):\n",
                                solver_recurse_depth*4, "",
-                               x, y, grid(x, y), isadjacent ? "|" : "!|", nx, ny);
+                               x+1, y+1, grid(x, y), isadjacent ? "|" : "!|", nx+1, ny+1);
                         printf("%*s  ruling out %d at (%d,%d)\n",
-                               solver_recurse_depth*4, "", n+1, nx, ny);
+                               solver_recurse_depth*4, "", n+1, nx+1, ny+1);
                     }
 #endif
                     cube(nx, ny, n+1) = FALSE;
@@ -730,10 +716,10 @@ static int solver_adjacent(game_solver *usolver)
     return nchanged;
 }
 
-static int solver_adjacent_set(game_solver *usolver)
+static int solver_adjacent_set(struct latin_solver *solver, void *vctx)
 {
-    struct latin_solver *solver = &usolver->latin;
-    int x, y, i, n, nn, o = usolver->latin.o, nx, ny, gd;
+    struct solver_ctx *ctx = (struct solver_ctx *)vctx;
+    int x, y, i, n, nn, o = solver->o, nx, ny, gd;
     int nchanged = 0, *scratch = snewn(o, int);
 
     /* Update possible values based on other possible values
@@ -741,8 +727,8 @@ static int solver_adjacent_set(game_solver *usolver)
 
     for (x = 0; x < o; x++) {
         for (y = 0; y < o; y++) {
-            for (i = 0; i < o; i++) {
-                int isadjacent = (GRID(usolver->state, flags, x, y) & adjthan[i].f);
+            for (i = 0; i < 4; i++) {
+                int isadjacent = (GRID(ctx->state, flags, x, y) & adjthan[i].f);
 
                 nx = x + adjthan[i].dx, ny = y + adjthan[i].dy;
                 if (nx < 0 || ny < 0 || nx >= o || ny >= o)
@@ -779,9 +765,9 @@ static int solver_adjacent_set(game_solver *usolver)
                     if (solver_show_working) {
                         printf("%*sadjacent possible elimination, (%d,%d) %s (%d,%d):\n",
                                solver_recurse_depth*4, "",
-                               x, y, isadjacent ? "|" : "!|", nx, ny);
+                               x+1, y+1, isadjacent ? "|" : "!|", nx+1, ny+1);
                         printf("%*s  ruling out %d at (%d,%d)\n",
-                               solver_recurse_depth*4, "", n+1, nx, ny);
+                               solver_recurse_depth*4, "", n+1, nx+1, ny+1);
                     }
 #endif
                     cube(nx, ny, n+1) = FALSE;
@@ -794,147 +780,45 @@ static int solver_adjacent_set(game_solver *usolver)
     return nchanged;
 }
 
-static int solver_grid(digit *grid, int o, int maxdiff, void *ctx)
+static int solver_easy(struct latin_solver *solver, void *vctx)
 {
-    game_state *state = (game_state *)ctx;
-    game_solver *solver;
-    struct latin_solver *lsolver;
-    struct latin_solver_scratch *scratch;
-    int ret, diff = DIFF_LATIN;
-
-    assert(maxdiff <= DIFF_RECURSIVE);
-
-    assert(state->order == o);
-    solver = new_solver(grid, state);
-
-    lsolver = &solver->latin;
-    scratch = latin_solver_new_scratch(lsolver);
-
-    while (1) {
-cont:
-        ret = latin_solver_diff_simple(lsolver);
-        if (ret < 0) {
-            diff = DIFF_IMPOSSIBLE;
-            goto got_result;
-        } else if (ret > 0) {
-            diff = max(diff, DIFF_LATIN);
-            goto cont;
-        }
-
-        if (maxdiff <= DIFF_LATIN)
-            break;
-
-        if (state->adjacent) {
-            /* Adjacent-specific: set possibles from known numbers
-             * and adjacency clues. */
-            ret = solver_adjacent(solver);
-        } else {
-            /* Unequal-specific: set possibles from chains of
-             * inequalities. */
-            ret = solver_links(solver);
-        }
-        if (ret < 0) {
-            diff = DIFF_IMPOSSIBLE;
-            goto got_result;
-        } else if (ret > 0) {
-            diff = max(diff, DIFF_EASY);
-            goto cont;
-        }
-
-        if (maxdiff <= DIFF_EASY)
-            break;
-
-        /* Row- and column-wise set elimination */
-        ret = latin_solver_diff_set(lsolver, scratch, 0);
-        if (ret < 0) {
-            diff = DIFF_IMPOSSIBLE;
-            goto got_result;
-        } else if (ret > 0) {
-            diff = max(diff, DIFF_SET);
-            goto cont;
-        }
-
-        if (state->adjacent) {
-            /* Adjacent-specific: set possibles from other possibles
-             * and adjacency clues. */
-            ret = solver_adjacent_set(solver);
-            if (ret < 0) {
-                diff = DIFF_IMPOSSIBLE;
-                goto got_result;
-            } else if (ret > 0) {
-                diff = max(diff, DIFF_SET);
-                goto cont;
-            }
-        }
-
-        if (maxdiff <= DIFF_SET)
-            break;
+    struct solver_ctx *ctx = (struct solver_ctx *)vctx;
+    if (ctx->state->adjacent)
+       return solver_adjacent(solver, vctx);
+    else
+       return solver_links(solver, vctx);
+}
 
-        ret = latin_solver_diff_set(lsolver, scratch, 1);
-        if (ret < 0) {
-            diff = DIFF_IMPOSSIBLE;
-            goto got_result;
-        } else if (ret > 0) {
-            diff = max(diff, DIFF_EXTREME);
-            goto cont;
-        }
+static int solver_set(struct latin_solver *solver, void *vctx)
+{
+    struct solver_ctx *ctx = (struct solver_ctx *)vctx;
+    if (ctx->state->adjacent)
+       return solver_adjacent_set(solver, vctx);
+    else
+       return 0;
+}
 
-        /*
-         * Forcing chains.
-         */
-        if (latin_solver_forcing(lsolver, scratch)) {
-            diff = max(diff, DIFF_EXTREME);
-            goto cont;
-        }
+#define SOLVER(upper,title,func,lower) func,
+static usersolver_t const unequal_solvers[] = { DIFFLIST(SOLVER) };
 
-        /*
-         * If we reach here, we have made no deductions in this
-         * iteration, so the algorithm terminates.
-         */
-        break;
-    }
-    /*
-     * Last chance: if we haven't fully solved the puzzle yet, try
-     * recursing based on guesses for a particular square. We pick
-     * one of the most constrained empty squares we can find, which
-     * has the effect of pruning the search tree as much as
-     * possible.
-     */
-    if (maxdiff == DIFF_RECURSIVE) {
-        int nsol = latin_solver_recurse(lsolver, DIFF_RECURSIVE, solver_grid, ctx);
-        if (nsol < 0) diff = DIFF_IMPOSSIBLE;
-        else if (nsol == 1) diff = DIFF_RECURSIVE;
-        else if (nsol > 1) diff = DIFF_AMBIGUOUS;
-        /* if nsol == 0 then we were complete anyway
-         * (and thus don't need to change diff) */
-    } else {
-        int cc = check_complete(grid, state, 0);
-        if (cc == -1) diff = DIFF_IMPOSSIBLE;
-        if (cc == 0) diff = DIFF_UNFINISHED;
-    }
+static int solver_state(game_state *state, int maxdiff)
+{
+    struct solver_ctx *ctx = new_ctx(state);
+    struct latin_solver solver;
+    int diff;
 
-got_result:
+    latin_solver_alloc(&solver, state->nums, state->order);
 
-#ifdef STANDALONE_SOLVER
-    if (solver_show_working)
-        printf("%*s%s found\n",
-               solver_recurse_depth*4, "",
-               diff == DIFF_IMPOSSIBLE ? "no solution (impossible)" :
-               diff == DIFF_UNFINISHED ? "no solution (unfinished)" :
-               diff == DIFF_AMBIGUOUS ? "multiple solutions" :
-               "one solution");
-#endif
+    diff = latin_solver_main(&solver, maxdiff,
+                            DIFF_LATIN, DIFF_SET, DIFF_EXTREME,
+                            DIFF_EXTREME, DIFF_RECURSIVE,
+                            unequal_solvers, ctx, clone_ctx, free_ctx);
 
-    latin_solver_free_scratch(scratch);
-    memcpy(state->hints, solver->latin.cube, o*o*o);
-    free_solver(solver);
+    memcpy(state->hints, solver.cube, state->order*state->order*state->order);
 
-    return diff;
-}
+    free_ctx(ctx);
 
-static int solver_state(game_state *state, int maxdiff)
-{
-    int diff = solver_grid(state->nums, state->order, maxdiff, (void*)state);
+    latin_solver_free(&solver);
 
     if (diff == DIFF_IMPOSSIBLE)
         return -1;
@@ -945,7 +829,8 @@ static int solver_state(game_state *state, int maxdiff)
     return 1;
 }
 
-static game_state *solver_hint(game_state *state, int *diff_r, int mindiff, int maxdiff)
+static game_state *solver_hint(const game_state *state, int *diff_r,
+                               int mindiff, int maxdiff)
 {
     game_state *ret = dup_game(state);
     int diff, r = 0;
@@ -991,7 +876,7 @@ static int gg_place_clue(game_state *state, int ccode, digit *latin, int checkon
 #ifdef STANDALONE_SOLVER
             if (state->nums[loc] != latin[loc]) {
                 printf("inconsistency for (%d,%d): state %d latin %d\n",
-                       x, y, state->nums[loc], latin[loc]);
+                       x+1, y+1, state->nums[loc], latin[loc]);
             }
 #endif
             assert(state->nums[loc] == latin[loc]);
@@ -1042,7 +927,7 @@ static int gg_remove_clue(game_state *state, int ccode, int checkonly)
 #ifdef STANDALONE_SOLVER
             if (solver_show_working)
                 printf("gg_remove_clue: removing %d at (%d,%d)",
-                       state->nums[loc], x, y);
+                       state->nums[loc], x+1, y+1);
 #endif
             state->nums[loc] = 0;
         }
@@ -1055,7 +940,7 @@ static int gg_remove_clue(game_state *state, int ccode, int checkonly)
 #ifdef STANDALONE_SOLVER
             if (solver_show_working)
                printf("gg_remove_clue: removing %c at (%d,%d)",
-                       adjthan[which].c, x, y);
+                       adjthan[which].c, x+1, y+1);
 #endif
             state->flags[loc] &= ~adjthan[which].f;
         }
@@ -1067,7 +952,7 @@ static int gg_best_clue(game_state *state, int *scratch, digit *latin)
 {
     int ls = state->order * state->order * 5;
     int maxposs = 0, minclues = 5, best = -1, i, j;
-    int nposs, nclues, loc, x, y;
+    int nposs, nclues, loc;
 
 #ifdef STANDALONE_SOLVER
     if (solver_show_working) {
@@ -1080,7 +965,6 @@ static int gg_best_clue(game_state *state, int *scratch, digit *latin)
         if (!gg_place_clue(state, scratch[i], latin, 1)) continue;
 
         loc = scratch[i] / 5;
-        x = loc % state->order; y = loc / state->order;
         for (j = nposs = 0; j < state->order; j++) {
             if (state->hints[loc*state->order + j]) nposs++;
         }
@@ -1091,9 +975,11 @@ static int gg_best_clue(game_state *state, int *scratch, digit *latin)
             (nposs == maxposs && nclues < minclues)) {
             best = i; maxposs = nposs; minclues = nclues;
 #ifdef STANDALONE_SOLVER
-            if (solver_show_working)
+            if (solver_show_working) {
+                int x = loc % state->order, y = loc / state->order;
                 printf("gg_best_clue: b%d (%d,%d) new best [%d poss, %d clues].\n",
-                       best, x, y, nposs, nclues);
+                       best, x+1, y+1, nposs, nclues);
+            }
 #endif
         }
     }
@@ -1209,9 +1095,11 @@ static void add_adjacent_flags(game_state *state, digit *latin)
     }
 }
 
-static char *new_game_desc(game_params *params, random_state *rs,
+static char *new_game_desc(const game_params *params_in, random_state *rs,
                           char **aux, int interactive)
 {
+    game_params params_copy = *params_in; /* structure copy */
+    game_params *params = &params_copy;
     digit *sq = NULL;
     int i, x, y, retlen, k, nsol;
     int o2 = params->order * params->order, ntries = 1;
@@ -1303,11 +1191,11 @@ generate:
     return ret;
 }
 
-static game_state *load_game(game_params *params, char *desc,
+static game_state *load_game(const game_params *params, const char *desc,
                              char **why_r)
 {
     game_state *state = blank_game(params->order, params->adjacent);
-    char *p = desc;
+    const char *p = desc;
     int i = 0, n, o = params->order, x, y;
     char *why = NULL;
 
@@ -1389,7 +1277,8 @@ fail:
     return NULL;
 }
 
-static game_state *new_game(midend *me, game_params *params, char *desc)
+static game_state *new_game(midend *me, const game_params *params,
+                            const char *desc)
 {
     game_state *state = load_game(params, desc, NULL);
     if (!state) {
@@ -1399,7 +1288,7 @@ static game_state *new_game(midend *me, game_params *params, char *desc)
     return state;
 }
 
-static char *validate_desc(game_params *params, char *desc)
+static char *validate_desc(const game_params *params, const char *desc)
 {
     char *why = NULL;
     game_state *dummy = load_game(params, desc, &why);
@@ -1411,8 +1300,8 @@ static char *validate_desc(game_params *params, char *desc)
     return why;
 }
 
-static char *solve_game(game_state *state, game_state *currstate,
-                       char *aux, char **error)
+static char *solve_game(const game_state *state, const game_state *currstate,
+                        const char *aux, char **error)
 {
     game_state *solved;
     int r;
@@ -1425,7 +1314,7 @@ static char *solve_game(game_state *state, game_state *currstate,
         if (!(solved->flags[r] & F_IMMUTABLE))
             solved->nums[r] = 0;
     }
-    r = solver_state(solved, DIFFCOUNT);
+    r = solver_state(solved, DIFFCOUNT-1);   /* always use full solver */
     if (r > 0) ret = latin_desc(solved->nums, solved->order);
     free_game(solved);
     return ret;
@@ -1440,7 +1329,7 @@ struct game_ui {
     int hshow, hpencil, hcursor;        /* show state, type, and ?cursor. */
 };
 
-static game_ui *new_ui(game_state *state)
+static game_ui *new_ui(const game_state *state)
 {
     game_ui *ui = snew(game_ui);
 
@@ -1455,17 +1344,17 @@ static void free_ui(game_ui *ui)
     sfree(ui);
 }
 
-static char *encode_ui(game_ui *ui)
+static char *encode_ui(const game_ui *ui)
 {
     return NULL;
 }
 
-static void decode_ui(game_ui *ui, char *encoding)
+static void decode_ui(game_ui *ui, const char *encoding)
 {
 }
 
-static void game_changed_state(game_ui *ui, game_state *oldstate,
-                               game_state *newstate)
+static void game_changed_state(game_ui *ui, const game_state *oldstate,
+                               const game_state *newstate)
 {
     /* See solo.c; if we were pencil-mode highlighting and
      * somehow a square has just been properly filled, cancel
@@ -1486,8 +1375,9 @@ struct game_drawstate {
     int hflash;
 };
 
-static char *interpret_move(game_state *state, game_ui *ui, game_drawstate *ds,
-                           int ox, int oy, int button)
+static char *interpret_move(const game_state *state, game_ui *ui,
+                            const game_drawstate *ds,
+                            int ox, int oy, int button)
 {
     int x = FROMCOORD(ox), y = FROMCOORD(oy), n;
     char buf[80];
@@ -1537,18 +1427,15 @@ static char *interpret_move(game_state *state, game_ui *ui, game_drawstate *ds,
         return "";
     }
 
-
-    if (ui->hshow) {
+    n = c2n(button, state->order);
+    if (ui->hshow && n >= 0 && n <= ds->order) {
         debug(("button %d, cbutton %d", button, (int)((char)button)));
-        n = c2n(button, state->order);
 
         debug(("n %d, h (%d,%d) p %d flags 0x%x nums %d",
                n, ui->hx, ui->hy, ui->hpencil,
                GRID(state, flags, ui->hx, ui->hy),
                GRID(state, nums, ui->hx, ui->hy)));
 
-        if (n < 0 || n > ds->order)
-            return NULL;        /* out of range */
         if (GRID(state, flags, ui->hx, ui->hy) & F_IMMUTABLE)
             return NULL;        /* can't edit immutable square (!) */
         if (ui->hpencil && GRID(state, nums, ui->hx, ui->hy) > 0)
@@ -1571,7 +1458,7 @@ static char *interpret_move(game_state *state, game_ui *ui, game_drawstate *ds,
     return NULL;
 }
 
-static game_state *execute_move(game_state *state, char *move)
+static game_state *execute_move(const game_state *state, const char *move)
 {
     game_state *ret = NULL;
     int x, y, n, i, rc;
@@ -1596,7 +1483,7 @@ static game_state *execute_move(game_state *state, char *move)
         }
         return ret;
     } else if (move[0] == 'S') {
-        char *p;
+        const char *p;
 
         ret = dup_game(state);
         ret->completed = ret->cheated = TRUE;
@@ -1638,8 +1525,8 @@ badmove:
 
 #define DRAW_SIZE (TILE_SIZE*ds->order + GAP_SIZE*(ds->order-1) + BORDER*2)
 
-static void game_compute_size(game_params *params, int tilesize,
-                             int *x, int *y)
+static void game_compute_size(const game_params *params, int tilesize,
+                              int *x, int *y)
 {
     /* Ick: fake up `ds->tilesize' for macro expansion purposes */
     struct { int tilesize, order; } ads, *ds = &ads;
@@ -1650,7 +1537,7 @@ static void game_compute_size(game_params *params, int tilesize,
 }
 
 static void game_set_size(drawing *dr, game_drawstate *ds,
-                         game_params *params, int tilesize)
+                          const game_params *params, int tilesize)
 {
     ds->tilesize = tilesize;
 }
@@ -1684,7 +1571,7 @@ static float *game_colours(frontend *fe, int *ncolours)
     return ret;
 }
 
-static game_drawstate *game_new_drawstate(drawing *dr, game_state *state)
+static game_drawstate *game_new_drawstate(drawing *dr, const game_state *state)
 {
     struct game_drawstate *ds = snew(struct game_drawstate);
     int o2 = state->order*state->order, o3 = o2*state->order;
@@ -1717,41 +1604,58 @@ static void game_free_drawstate(drawing *dr, game_drawstate *ds)
 static void draw_gt(drawing *dr, int ox, int oy,
                     int dx1, int dy1, int dx2, int dy2, int col)
 {
-    draw_line(dr, ox, oy, ox+dx1, oy+dy1, col);
-    draw_line(dr, ox+dx1, oy+dy1, ox+dx1+dx2, oy+dy1+dy2, col);
+    int coords[12];
+    int xdx = (dx1+dx2 ? 0 : 1), xdy = (dx1+dx2 ? 1 : 0);
+    coords[0] = ox + xdx;
+    coords[1] = oy + xdy;
+    coords[2] = ox + xdx + dx1;
+    coords[3] = oy + xdy + dy1;
+    coords[4] = ox + xdx + dx1 + dx2;
+    coords[5] = oy + xdy + dy1 + dy2;
+    coords[6] = ox - xdx + dx1 + dx2;
+    coords[7] = oy - xdy + dy1 + dy2;
+    coords[8] = ox - xdx + dx1;
+    coords[9] = oy - xdy + dy1;
+    coords[10] = ox - xdx;
+    coords[11] = oy - xdy;
+    draw_polygon(dr, coords, 6, col, col);
 }
 
 static void draw_gts(drawing *dr, game_drawstate *ds, int ox, int oy,
-                     unsigned int f, int col)
+                     unsigned int f, int bg, int fg)
 {
     int g = GAP_SIZE, g2 = (g+1)/2, g4 = (g+1)/4;
 
     /* Draw all the greater-than signs emanating from this tile. */
 
     if (f & F_ADJ_UP) {
+       if (bg >= 0) draw_rect(dr, ox, oy - g, TILE_SIZE, g, bg);
         draw_gt(dr, ox+g2, oy-g4, g2, -g2, g2, g2,
-               (f & F_ERROR_UP) ? COL_ERROR : col);
+               (f & F_ERROR_UP) ? COL_ERROR : fg);
         draw_update(dr, ox, oy-g, TILE_SIZE, g);
     }
     if (f & F_ADJ_RIGHT) {
+       if (bg >= 0) draw_rect(dr, ox + TILE_SIZE, oy, g, TILE_SIZE, bg);
         draw_gt(dr, ox+TILE_SIZE+g4, oy+g2, g2, g2, -g2, g2,
-                (f & F_ERROR_RIGHT) ? COL_ERROR : col);
+                (f & F_ERROR_RIGHT) ? COL_ERROR : fg);
         draw_update(dr, ox+TILE_SIZE, oy, g, TILE_SIZE);
     }
     if (f & F_ADJ_DOWN) {
+       if (bg >= 0) draw_rect(dr, ox, oy + TILE_SIZE, TILE_SIZE, g, bg);
         draw_gt(dr, ox+g2, oy+TILE_SIZE+g4, g2, g2, g2, -g2,
-               (f & F_ERROR_DOWN) ? COL_ERROR : col);
+               (f & F_ERROR_DOWN) ? COL_ERROR : fg);
         draw_update(dr, ox, oy+TILE_SIZE, TILE_SIZE, g);
     }
     if (f & F_ADJ_LEFT) {
+       if (bg >= 0) draw_rect(dr, ox - g, oy, g, TILE_SIZE, bg);
         draw_gt(dr, ox-g4, oy+g2, -g2, g2, g2, g2,
-                (f & F_ERROR_LEFT) ? COL_ERROR : col);
+                (f & F_ERROR_LEFT) ? COL_ERROR : fg);
         draw_update(dr, ox-g, oy, g, TILE_SIZE);
     }
 }
 
 static void draw_adjs(drawing *dr, game_drawstate *ds, int ox, int oy,
-                     unsigned int f, int col)
+                      unsigned int f, int bg, int fg)
 {
     int g = GAP_SIZE, g38 = 3*(g+1)/8, g4 = (g+1)/4;
 
@@ -1765,30 +1669,31 @@ static void draw_adjs(drawing *dr, game_drawstate *ds, int ox, int oy,
     if (f & (F_ADJ_RIGHT|F_ERROR_RIGHT)) {
         if (f & F_ADJ_RIGHT) {
             draw_rect(dr, ox+TILE_SIZE+g38, oy, g4, TILE_SIZE,
-                      (f & F_ERROR_RIGHT) ? COL_ERROR : col);
+                      (f & F_ERROR_RIGHT) ? COL_ERROR : fg);
         } else {
             draw_rect_outline(dr, ox+TILE_SIZE+g38, oy, g4, TILE_SIZE, COL_ERROR);
         }
-    } else {
-        draw_rect(dr, ox+TILE_SIZE+g38, oy, g4, TILE_SIZE, COL_BACKGROUND);
+    } else if (bg >= 0) {
+        draw_rect(dr, ox+TILE_SIZE+g38, oy, g4, TILE_SIZE, bg);
     }
     draw_update(dr, ox+TILE_SIZE, oy, g, TILE_SIZE);
 
     if (f & (F_ADJ_DOWN|F_ERROR_DOWN)) {
         if (f & F_ADJ_DOWN) {
             draw_rect(dr, ox, oy+TILE_SIZE+g38, TILE_SIZE, g4,
-                      (f & F_ERROR_DOWN) ? COL_ERROR : col);
+                      (f & F_ERROR_DOWN) ? COL_ERROR : fg);
         } else {
             draw_rect_outline(dr, ox, oy+TILE_SIZE+g38, TILE_SIZE, g4, COL_ERROR);
         }
-    } else {
-        draw_rect(dr, ox, oy+TILE_SIZE+g38, TILE_SIZE, g4, COL_BACKGROUND);
+    } else if (bg >= 0) {
+        draw_rect(dr, ox, oy+TILE_SIZE+g38, TILE_SIZE, g4, bg);
     }
     draw_update(dr, ox, oy+TILE_SIZE, TILE_SIZE, g);
 }
 
-static void draw_furniture(drawing *dr, game_drawstate *ds, game_state *state,
-                           game_ui *ui, int x, int y, int hflash)
+static void draw_furniture(drawing *dr, game_drawstate *ds,
+                           const game_state *state, const game_ui *ui,
+                           int x, int y, int hflash)
 {
     int ox = COORD(x), oy = COORD(y), bg, hon;
     unsigned int f = GRID(state, flags, x, y);
@@ -1820,9 +1725,9 @@ static void draw_furniture(drawing *dr, game_drawstate *ds, game_state *state,
 
     /* Draw the adjacent clue signs. */
     if (ds->adjacent)
-        draw_adjs(dr, ds, ox, oy, f, COL_GRID);
+        draw_adjs(dr, ds, ox, oy, f, COL_BACKGROUND, COL_GRID);
     else
-        draw_gts(dr, ds, ox, oy, f, COL_TEXT);
+        draw_gts(dr, ds, ox, oy, f, COL_BACKGROUND, COL_TEXT);
 }
 
 static void draw_num(drawing *dr, game_drawstate *ds, int x, int y)
@@ -1878,9 +1783,10 @@ static void draw_hints(drawing *dr, game_drawstate *ds, int x, int y)
     }
 }
 
-static void game_redraw(drawing *dr, game_drawstate *ds, game_state *oldstate,
-                       game_state *state, int dir, game_ui *ui,
-                       float animtime, float flashtime)
+static void game_redraw(drawing *dr, game_drawstate *ds,
+                        const game_state *oldstate, const game_state *state,
+                        int dir, const game_ui *ui,
+                        float animtime, float flashtime)
 {
     int x, y, i, hchanged = 0, stale, hflash = 0;
 
@@ -1948,14 +1854,14 @@ static void game_redraw(drawing *dr, game_drawstate *ds, game_state *oldstate,
     ds->hflash = hflash;
 }
 
-static float game_anim_length(game_state *oldstate, game_state *newstate,
-                             int dir, game_ui *ui)
+static float game_anim_length(const game_state *oldstate,
+                              const game_state *newstate, int dir, game_ui *ui)
 {
     return 0.0F;
 }
 
-static float game_flash_length(game_state *oldstate, game_state *newstate,
-                              int dir, game_ui *ui)
+static float game_flash_length(const game_state *oldstate,
+                               const game_state *newstate, int dir, game_ui *ui)
 {
     if (!oldstate->completed && newstate->completed &&
         !oldstate->cheated && !newstate->cheated)
@@ -1963,12 +1869,17 @@ static float game_flash_length(game_state *oldstate, game_state *newstate,
     return 0.0F;
 }
 
-static int game_timing_state(game_state *state, game_ui *ui)
+static int game_status(const game_state *state)
+{
+    return state->completed ? +1 : 0;
+}
+
+static int game_timing_state(const game_state *state, game_ui *ui)
 {
     return TRUE;
 }
 
-static void game_print_size(game_params *params, float *x, float *y)
+static void game_print_size(const game_params *params, float *x, float *y)
 {
     int pw, ph;
 
@@ -1978,7 +1889,7 @@ static void game_print_size(game_params *params, float *x, float *y)
     *y = ph / 100.0F;
 }
 
-static void game_print(drawing *dr, game_state *state, int tilesize)
+static void game_print(drawing *dr, const game_state *state, int tilesize)
 {
     int ink = print_mono_colour(dr, 0);
     int x, y, o = state->order, ox, oy, n;
@@ -2004,10 +1915,10 @@ static void game_print(drawing *dr, game_state *state, int tilesize)
                       FONT_VARIABLE, TILE_SIZE/2, ALIGN_VCENTRE | ALIGN_HCENTRE,
                       ink, str);
 
-            if (ds->adjacent)
-                draw_adjs(dr, ds, ox, oy, GRID(state, flags, x, y), ink);
+            if (state->adjacent)
+                draw_adjs(dr, ds, ox, oy, GRID(state, flags, x, y), -1, ink);
             else
-                draw_gts(dr, ds, ox, oy, GRID(state, flags, x, y), ink);
+                draw_gts(dr, ds, ox, oy, GRID(state, flags, x, y), -1, ink);
         }
     }
 }
@@ -2051,6 +1962,7 @@ const struct game thegame = {
     game_redraw,
     game_anim_length,
     game_flash_length,
+    game_status,
     TRUE, FALSE, game_print_size, game_print,
     FALSE,                            /* wants_statusbar */
     FALSE, game_timing_state,
@@ -2126,17 +2038,29 @@ static void pdiff(int diff)
 
 static int solve(game_params *p, char *desc, int debug)
 {
-    game_state *st = new_game(NULL, p, desc);
+    game_state *state = new_game(NULL, p, desc);
+    struct solver_ctx *ctx = new_ctx(state);
+    struct latin_solver solver;
     int diff;
 
     solver_show_working = debug;
-    game_debug(st);
+    game_debug(state);
+
+    latin_solver_alloc(&solver, state->nums, state->order);
+
+    diff = latin_solver_main(&solver, DIFF_RECURSIVE,
+                            DIFF_LATIN, DIFF_SET, DIFF_EXTREME,
+                            DIFF_EXTREME, DIFF_RECURSIVE,
+                            unequal_solvers, ctx, clone_ctx, free_ctx);
+
+    free_ctx(ctx);
+
+    latin_solver_free(&solver);
 
-    diff = solver_grid(st->nums, st->order, DIFF_RECURSIVE, (void*)st);
     if (debug) pdiff(diff);
 
-    game_debug(st);
-    free_game(st);
+    game_debug(state);
+    free_game(state);
     return diff;
 }