Allow more general cross-shaped boards in Pegs

I found a plausible looking Web page claiming that various different
sizes of cross are soluble, and some of them are quite widespread.  I've
enabled the ones that are symmetric enough that the existing game
generator can lay them out.

1 files changed, 29 insertions, 5 deletions

diff --git a/pegs.c b/pegs.c
index 2005a9e..1cfa9c7 100644
--- a/pegs.c
+++ b/pegs.c
@@ -71,7 +71,11 @@ static game_params *default_params(void)
 }
 
 static const struct game_params pegs_presets[] = {
+    {5, 7, TYPE_CROSS},
     {7, 7, TYPE_CROSS},
+    {5, 9, TYPE_CROSS},
+    {7, 9, TYPE_CROSS},
+    {9, 9, TYPE_CROSS},
     {7, 7, TYPE_OCTAGON},
     {5, 5, TYPE_RANDOM},
     {7, 7, TYPE_RANDOM},
@@ -90,7 +94,7 @@ static bool game_fetch_preset(int i, char **name, game_params **params)
     *ret = pegs_presets[i];
 
     strcpy(str, pegs_titletypes[ret->type]);
-    if (ret->type == TYPE_RANDOM)
+    if (ret->type == TYPE_CROSS || ret->type == TYPE_RANDOM)
 	sprintf(str + strlen(str), " %dx%d", ret->w, ret->h);
 
     *name = dupstr(str);
@@ -189,12 +193,32 @@ static const char *validate_params(const game_params *params, bool full)
         return "Width times height must not be unreasonably large";
 
     /*
-     * It might be possible to implement generalisations of Cross
-     * and Octagon, but only if I can find a proof that they're all
+     * At http://www.gibell.net/pegsolitaire/GenCross/GenCrossBoards0.html
+     * George I. Bell asserts that various generalised cross-shaped
+     * boards are soluble starting (and finishing) with the centre
+     * hole.  We permit the symmetric ones.  Bell's notation for each
+     * soluble board is listed.
+     */
+    if (full && params->type == TYPE_CROSS) {
+        if (!((params->w == 9 && params->h == 5) || /* (3,1,3,1) */
+              (params->w == 5 && params->h == 9) || /* (1,3,1,3) */
+              (params->w == 9 && params->h == 9) || /* (3,3,3,3) */
+              (params->w == 7 && params->h == 5) || /* (2,1,2,1) */
+              (params->w == 5 && params->h == 7) || /* (1,2,1,2) */
+              (params->w == 9 && params->h == 7) || /* (3,2,3,2) */
+              (params->w == 7 && params->h == 9) || /* (2,3,2,3) */
+              (params->w == 7 && params->h == 7)))  /* (2,2,2,2) */
+            return "This board type is only supported at "
+                "5x7, 5x9, 7x7, 7x9, and 9x9";
+    }
+
+    /*
+     * It might be possible to implement generalisations of
+     * Octagon, but only if I can find a proof that they're all
      * soluble. For the moment, therefore, I'm going to disallow
-     * them at any size other than the standard one.
+     * it at any size other than the standard one.
      */
-    if (full && (params->type == TYPE_CROSS || params->type == TYPE_OCTAGON)) {
+    if (full && params->type == TYPE_OCTAGON) {
 	if (params->w != 7 || params->h != 7)
 	    return "This board type is only supported at 7x7";
     }