ref: 739609cec2262017aaabb7e34ce75af784fd683c
parent: c11f9ff173763e92155838d79a5ea130c5693540
author: Simon Tatham <anakin@pobox.com>
date: Tue May 31 14:09:28 EDT 2005
Aha! It turns out, after a bit of failure-mode profiling, that when the Mines unique grid generator fails at high mine densities it is _almost always_ for the same reason, and it also turns out that this reason is one which can be addressed. So here's an enhancement to mineperturb() which enables Mines to generate a grid at (as far as I can tell) any mine density you like, up to and including w*h-9 mines. At densities of 1 in 2 or thereabouts the grids start to look rather strange, but it can at least generate them without hanging. [originally from svn r5885]
--- a/mines.c
+++ b/mines.c
@@ -10,14 +10,8 @@
* That hook can talk to the game_ui and set the cheated flag,
* and then make_move can avoid setting the `won' flag after that.
*
- * - question marks (arrgh, preferences?)
- *
- * - sensible parameter constraints
- * + 30x16: 191 mines just about works if rather slowly, 192 is
- * just about doom (the latter corresponding to a density of
- * exactly 1 in 2.5)
- * + 9x9: 45 mines works - over 1 in 2! 50 seems a bit slow.
- * + it might not be feasible to work out the exact limit
+ * - think about configurably supporting question marks. Once,
+ * that is, we've thought about configurability in general!
*/
#include <stdio.h>
@@ -1166,13 +1160,18 @@
*
* If we have no sets at all, we must give up.
*/
- if (count234(ss->sets) == 0)
- break;
- s = index234(ss->sets, random_upto(rs, count234(ss->sets)));
+ if (count234(ss->sets) == 0) {#ifdef SOLVER_DIAGNOSTICS
- printf("perturbing on set %d,%d %03x\n", s->x, s->y, s->mask);+ printf("perturbing on entire unknown set\n");#endif
- ret = perturb(ctx, grid, s->x, s->y, s->mask);
+ ret = perturb(ctx, grid, 0, 0, 0);
+ } else {+ s = index234(ss->sets, random_upto(rs, count234(ss->sets)));
+#ifdef SOLVER_DIAGNOSTICS
+ printf("perturbing on set %d,%d %03x\n", s->x, s->y, s->mask);+#endif
+ ret = perturb(ctx, grid, s->x, s->y, s->mask);
+ }
if (ret) {assert(ret->n > 0); /* otherwise should have been NULL */
@@ -1182,6 +1181,8 @@
* the returned structure tells us which. Adjust
* the mine count in any set which overlaps one of
* those squares, and put them back on the to-do
+ * list. Also, if the square itself is marked as a
+ * known non-mine, put it back on the squares-to-do
* list.
*/
for (i = 0; i < ret->n; i++) {@@ -1191,6 +1192,11 @@
ret->changes[i].x, ret->changes[i].y);
#endif
+ if (ret->changes[i].delta < 0 &&
+ grid[ret->changes[i].y*w+ret->changes[i].x] != -2) {+ std_add(std, ret->changes[i].y*w+ret->changes[i].x);
+ }
+
list = ss_overlap(ss,
ret->changes[i].x, ret->changes[i].y, 1);
@@ -1212,7 +1218,7 @@
/*
* Dump the current known state of the grid.
*/
- printf("state after perturbation:\n", nperturbs);+ printf("state after perturbation:\n"); for (y = 0; y < h; y++) { for (x = 0; x < w; x++) {int v = grid[y*w+x];
@@ -1284,6 +1290,7 @@
signed char *grid;
int w, h;
int sx, sy;
+ int allow_big_perturbs;
random_state *rs;
};
@@ -1340,6 +1347,22 @@
return 0;
}
+/*
+ * Normally this function is passed an (x,y,mask) set description.
+ * On occasions, though, there is no _localised_ set being used,
+ * and the set being perturbed is supposed to be the entirety of
+ * the unreachable area. This is signified by the special case
+ * mask==0: in this case, anything labelled -2 in the grid is part
+ * of the set.
+ *
+ * Allowing perturbation in this special case appears to make it
+ * guaranteeably possible to generate a workable grid for any mine
+ * density, but they tend to be a bit boring, with mines packed
+ * densely into far corners of the grid and the remainder being
+ * less dense than one might like. Therefore, to improve overall
+ * grid quality I disable this feature for the first few attempts,
+ * and fall back to it after no useful grid has been generated.
+ */
static struct perturbations *mineperturb(void *vctx, signed char *grid,
int setx, int sety, int mask)
{@@ -1346,10 +1369,14 @@
struct minectx *ctx = (struct minectx *)vctx;
struct square *sqlist;
int x, y, dx, dy, i, n, nfull, nempty;
- struct square *tofill[9], *toempty[9], **todo;
+ struct square **tofill, **toempty, **todo;
int ntofill, ntoempty, ntodo, dtodo, dset;
struct perturbations *ret;
+ int *setlist;
+ if (!mask && !ctx->allow_big_perturbs)
+ return NULL;
+
/*
* Make a list of all the squares in the grid which we can
* possibly use. This list should be in preference order, which
@@ -1379,9 +1406,10 @@
* If this square is in the input set, also don't put
* it on the list!
*/
- if (x >= setx && x < setx + 3 &&
- y >= sety && y < sety + 3 &&
- mask & (1 << ((y-sety)*3+(x-setx))))
+ if ((mask == 0 && grid[y*ctx->w+x] == -2) ||
+ (x >= setx && x < setx + 3 &&
+ y >= sety && y < sety + 3 &&
+ mask & (1 << ((y-sety)*3+(x-setx)))))
continue;
sqlist[n].x = x;
@@ -1424,16 +1452,27 @@
* we've been provided.
*/
nfull = nempty = 0;
- for (dy = 0; dy < 3; dy++)
- for (dx = 0; dx < 3; dx++)
- if (mask & (1 << (dy*3+dx))) {- assert(setx+dx <= ctx->w);
- assert(sety+dy <= ctx->h);
- if (ctx->grid[(sety+dy)*ctx->w+(setx+dx)])
- nfull++;
- else
- nempty++;
- }
+ if (mask) {+ for (dy = 0; dy < 3; dy++)
+ for (dx = 0; dx < 3; dx++)
+ if (mask & (1 << (dy*3+dx))) {+ assert(setx+dx <= ctx->w);
+ assert(sety+dy <= ctx->h);
+ if (ctx->grid[(sety+dy)*ctx->w+(setx+dx)])
+ nfull++;
+ else
+ nempty++;
+ }
+ } else {+ for (y = 0; y < ctx->h; y++)
+ for (x = 0; x < ctx->w; x++)
+ if (grid[y*ctx->w+x] == -2) {+ if (ctx->grid[y*ctx->w+x])
+ nfull++;
+ else
+ nempty++;
+ }
+ }
/*
* Now go through our sorted list until we find either `nfull'
@@ -1443,6 +1482,13 @@
* overall.
*/
ntofill = ntoempty = 0;
+ if (mask) {+ tofill = snewn(9, struct square *);
+ toempty = snewn(9, struct square *);
+ } else {+ tofill = snewn(ctx->w * ctx->h, struct square *);
+ toempty = snewn(ctx->w * ctx->h, struct square *);
+ }
for (i = 0; i < n; i++) {struct square *sq = &sqlist[i];
if (ctx->grid[sq->y * ctx->w + sq->x])
@@ -1454,13 +1500,56 @@
}
/*
- * If this didn't work at all, I think we just give up.
+ * If we haven't found enough empty squares outside the set to
+ * empty it into _or_ enough full squares outside it to fill it
+ * up with, we'll have to settle for doing only a partial job.
+ * In this case we choose to always _fill_ the set (because
+ * this case will tend to crop up when we're working with very
+ * high mine densities and the only way to get a solvable grid
+ * is going to be to pack most of the mines solidly around the
+ * edges). So now our job is to make a list of the empty
+ * squares in the set, and shuffle that list so that we fill a
+ * random selection of them.
*/
if (ntofill != nfull && ntoempty != nempty) {- sfree(sqlist);
- return NULL;
- }
+ int k;
+ assert(ntoempty != 0);
+
+ setlist = snewn(ctx->w * ctx->h, int);
+ i = 0;
+ if (mask) {+ for (dy = 0; dy < 3; dy++)
+ for (dx = 0; dx < 3; dx++)
+ if (mask & (1 << (dy*3+dx))) {+ assert(setx+dx <= ctx->w);
+ assert(sety+dy <= ctx->h);
+ if (!ctx->grid[(sety+dy)*ctx->w+(setx+dx)])
+ setlist[i++] = (sety+dy)*ctx->w+(setx+dx);
+ }
+ } else {+ for (y = 0; y < ctx->h; y++)
+ for (x = 0; x < ctx->w; x++)
+ if (grid[y*ctx->w+x] == -2) {+ if (!ctx->grid[y*ctx->w+x])
+ setlist[i++] = y*ctx->w+x;
+ }
+ }
+ assert(i > ntoempty);
+ /*
+ * Now pick `ntoempty' items at random from the list.
+ */
+ for (k = 0; k < ntoempty; k++) {+ int index = k + random_upto(ctx->rs, i - k);
+ int tmp;
+
+ tmp = setlist[k];
+ setlist[k] = setlist[index];
+ setlist[index] = tmp;
+ }
+ } else
+ setlist = NULL;
+
/*
* Now we're pretty much there. We need to either
* (a) put a mine in each of the empty squares in the set, and
@@ -1479,11 +1568,17 @@
ntodo = ntofill;
dtodo = +1;
dset = -1;
+ sfree(toempty);
} else {+ /*
+ * (We also fall into this case if we've constructed a
+ * setlist.)
+ */
todo = toempty;
ntodo = ntoempty;
dtodo = -1;
dset = +1;
+ sfree(tofill);
}
ret->n = 2 * ntodo;
ret->changes = snewn(ret->n, struct perturbation);
@@ -1493,20 +1588,45 @@
ret->changes[i].delta = dtodo;
}
/* now i == ntodo */
- for (dy = 0; dy < 3; dy++)
- for (dx = 0; dx < 3; dx++)
- if (mask & (1 << (dy*3+dx))) {- int currval = (ctx->grid[(sety+dy)*ctx->w+(setx+dx)] ? +1 : -1);
- if (dset == -currval) {- ret->changes[i].x = setx + dx;
- ret->changes[i].y = sety + dy;
- ret->changes[i].delta = dset;
- i++;
+ if (setlist) {+ int j;
+ assert(todo == toempty);
+ for (j = 0; j < ntoempty; j++) {+ ret->changes[i].x = setlist[j] % ctx->w;
+ ret->changes[i].y = setlist[j] / ctx->w;
+ ret->changes[i].delta = dset;
+ i++;
+ }
+ sfree(setlist);
+ } else if (mask) {+ for (dy = 0; dy < 3; dy++)
+ for (dx = 0; dx < 3; dx++)
+ if (mask & (1 << (dy*3+dx))) {+ int currval = (ctx->grid[(sety+dy)*ctx->w+(setx+dx)] ? +1 : -1);
+ if (dset == -currval) {+ ret->changes[i].x = setx + dx;
+ ret->changes[i].y = sety + dy;
+ ret->changes[i].delta = dset;
+ i++;
+ }
}
- }
+ } else {+ for (y = 0; y < ctx->h; y++)
+ for (x = 0; x < ctx->w; x++)
+ if (grid[y*ctx->w+x] == -2) {+ int currval = (ctx->grid[y*ctx->w+x] ? +1 : -1);
+ if (dset == -currval) {+ ret->changes[i].x = x;
+ ret->changes[i].y = y;
+ ret->changes[i].delta = dset;
+ i++;
+ }
+ }
+ }
assert(i == ret->n);
sfree(sqlist);
+ sfree(todo);
/*
* Having set up the precise list of changes we're going to
@@ -1593,9 +1713,11 @@
{char *ret = snewn(w*h, char);
int success;
+ int ntries = 0;
do {success = FALSE;
+ ntries++;
memset(ret, 0, w*h);
@@ -1670,6 +1792,7 @@
ctx->sx = x;
ctx->sy = y;
ctx->rs = rs;
+ ctx->allow_big_perturbs = (ntries > 100);
while (1) {memset(solvegrid, -2, w*h);