The Twiddle shuffling algorithm was theoretically parity-unbalanced:

[sgt/puzzles] / twiddle.c

diff --git a/twiddle.c b/twiddle.c
index 8a389b4..5209606 100644 (file)
--- a/twiddle.c
+++ b/twiddle.c
@@ -317,7 +317,7 @@ static char *new_game_seed(game_params *params, random_state *rs,
      * and simply shuffle the grid by making a long sequence of
      * randomly chosen moves.
      */
-    total_moves = w*h*n*n*2;
+    total_moves = w*h*n*n*2 + random_upto(rs, 1);
     for (i = 0; i < total_moves; i++) {
        int x, y;
 
@@ -479,6 +479,7 @@ static game_state *solve_game(game_state *state, game_aux_info *aux,
                              char **error)
 {
     game_state *ret = dup_game(state);
+    int i;
 
     /*
      * Simply replace the grid with a solved one. For this game,
@@ -488,6 +489,8 @@ static game_state *solve_game(game_state *state, game_aux_info *aux,
      * which to practise manoeuvres.
      */
     qsort(ret->grid, ret->w*ret->h, sizeof(int), compare_int);
+    for (i = 0; i < ret->w*ret->h; i++)
+       ret->grid[i] &= ~3;
     ret->used_solve = ret->just_used_solve = TRUE;
     ret->completed = ret->movecount;