YOKOC - Cubic Eight-Puzzle
Let's play a puzzle using eight cubes placed on a 3 x 3 board leaving one empty square.
Faces of cubes are painted with three colors. As a puzzle step, you can roll one of the cubes to the adjacent empty square. Your goal is to make the specified color pattern visible from above by a number of such steps.
The rules of this puzzle are as follows.
- Coloring of Cubes: All the cubes are colored in the same way as shown in Figure 3. The opposite faces have the same color.
Figure 3: Coloring of a cube
- Initial Board State: Eight cubes are placed on the 3 x 3 board leaving one empty square. All the cubes have the same orientation as shown in Figure 4. As shown in the figure, squares on the board are given x and y coordinates, (1, 1), (1, 2), ..., and (3, 3). The position of the initially empty square may vary.
Figure 4: Initial board state
- Rolling Cubes: At each step, we can choose one of the cubes adjacent to the empty square and roll it into the empty square, leaving the original position empty. Figure 5 shows an example.
Figure 5: Rolling a cube
- Goal: The goal of this puzzle is to arrange the cubes so that their top faces form the specified color pattern by a number of cube rolling steps described above.
Your task is to write a program that finds the minimum number of steps required to make the specified color pattern from the given initial state.
The input is a sequence of datasets. The end of the input is indicated by a line containing two zeros separated by a space. The number of datasets is less than 16. Each dataset is formatted as follows.
x y F11 F21 F31 F12 F22 F32 F13 F23 F33
The first line contains two integers x and y separated by a space, indicating the position (x, y) of the initially empty square. The values of x and y are 1, 2, or 3.
The following three lines specify the color pattern to make. Each line contains three characters F1j, F2j, and F3j, separated by a space. Character Fij indicates the top color of the cube, if any, at position (i, j) as follows:
- B: Blue,
- W: White,
- R: Red,
- E: the square is Empty.
There is exactly one `E' character in each dataset.
For each dataset, output the minimum number of steps to achieve the goal, when the goal can be reached within 30 steps. Otherwise, output ``-1'' for the dataset.
Input:1 2 W W W E W W W W W 2 1 R B W R W W E W W 3 3 W B W B R E R B R 3 3 B W R B W R B E R 2 1 B B B B R B B R E 1 1 R R R W W W R R E 2 1 R R R B W B R R E 3 2 R R R W E W R R R 0 0Output:0 3 13 23 29 30 -1 -1