UVa 704：Colour Hash, 雙向bfs

連結：

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=110&page=show_problem&problem=645

類型：隱式圖搜尋，雙向bfs

原題：

This puzzle consists of two wheels. Both wheels can rotate both clock and counter-clockwise. They contain 21 coloured pieces, 10 of which are rounded triangles and 11 of which are separators. Figure 1 shows the final position of each one of the pieces. Note that to perform a one step rotation you must turn the wheel until you have advanced a triangle and a separator.

Figure 1. Final puzzle configuration

Your job is to write a program that reads the puzzle configuration and prints the minimum sequence of movements required to reach the final position. We will use the following integer values to encode each type of piece:

0	grey separator
1	yellow triangle
2	yellow separator
3	cyan triangle
4	cyan separator
5	violet triangle
6	violet separator
7	green triangle
8	green separator
9	red triangle
10	red separator

A puzzle configuration will be described using 24 integers, the first 12 to describe the left wheel configuration and the last 12 for the right wheel. The first integer represents the bottom right separator of the left wheel and the next eleven integers describe the left wheel clockwise. The thirteenth integer represents the bottom left separator of right wheel and the next eleven integers describe the right wheel counter-clockwise.

The final position is therefore encoded like:

0 3 4 3 0 5 6 5 0 1 2 1 0 7 8 7 0 9 10 9 0 1 2 1

If for instance we rotate the left wheel clockwise one position from the final configuration (as shown in Figure 2) the puzzle configuration would be encoded like:

2 1 0 3 4 3 0 5 6 5 0 1 0 7 8 7 0 9 10 9 0 5 0 1

Figure 2. The puzzle after rotating the left wheel on step clockwise from the final configuration.