/* determine if puzzle is solvable */
   public static boolean isSolvable(int[] state) {
     int inversions = 0;
     for (int i = 0; i < state.length; i++)
       for (int j = i; j < state.length; j++)
         if (state[i] < state[j]) inversions++;

     System.out.println("Inversion: " + inversions);
     return true;
   }