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ref: 31cb5227e6df543a077910d0f3e7c7e169e7c01e
parent: f21d3e4c74b23380f397a7ee0416928ee971a15d
author: Simon Tatham <anakin@pobox.com>
date: Sat May 23 04:41:43 EDT 2020 

Group: fill in the latin.c validator function.

This actually fixes the example game id mentioned in the previous
commit. Now 12i:m12b9a1zd9i6d10c3y2l11q4r is reported as Unreasonable
rather than ambiguous, on the basis that although the solver still
recurses and finds two filled grids, the validator throws out the
nonsense one at the last minute, leaving only one that's actually
legal.


--- a/unfinished/group.c
+++ b/unfinished/group.c
@@ -450,7 +450,37 @@
 
 static bool group_valid(struct latin_solver *solver, void *ctx)
 {
-    return true;                       /* FIXME */
+    int w = solver->o;
+#ifdef STANDALONE_SOLVER
+    char **names = solver->names;
+#endif
+    int i, j, k;
+
+    for (i = 0; i < w; i++)
+	for (j = 0; j < w; j++)
+	    for (k = 0; k < w; k++) {
+                int ij = grid(i, j) - 1;
+                int jk = grid(j, k) - 1;
+                int ij_k = grid(ij, k) - 1;
+                int i_jk = grid(i, jk) - 1;
+                if (ij_k != i_jk) {
+#ifdef STANDALONE_SOLVER
+                    if (solver_show_working) {
+                        printf("%*sfailure of associativity: "
+                               "(%s%s)%s = %s%s = %s but "
+                               "%s(%s%s) = %s%s = %s\n",
+                               solver_recurse_depth*4, "",
+                               names[i], names[j], names[k],
+                               names[ij], names[k], names[ij_k],
+                               names[i], names[j], names[k],
+                               names[i], names[jk], names[i_jk]);
+                    }
+#endif
+                    return false;
+                }
+            }
+
+    return true;
 }
 
 static int solver(const game_params *params, digit *grid, int maxdiff)