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ref: c139aba078f2ec46a0e0b44142b7c982519a8263
parent: 97b03cc67a31c1d0869a21c50b9ca31f78775ff9
author: Ben Harris <bjh21@bjh21.me.uk>
date: Sat Feb 11 20:24:58 EST 2023 

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.


--- a/pegs.c
+++ b/pegs.c
@@ -71,7 +71,11 @@
 }
 
 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 @@
     *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 @@
         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";
     }
--- a/puzzles.but
+++ b/puzzles.but
@@ -1446,8 +1446,9 @@
 
 \dd Controls whether you are given a board of a standard shape or a
 randomly generated shape. The two standard shapes currently
-supported are \q{Cross} and \q{Octagon} (also commonly known as the
-English and European traditional board layouts respectively).
+supported are \q{Cross} (in various sizes) and \q{Octagon}.
+The 7\by\.7 Cross is the traditional English board layout.
+The Octagon is the traditional French one.
 Selecting \q{Random} will give you a different board shape every
 time (but always one that is known to have a solution).