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#3339. 八数码问题

Estadísticas

你刚给你的小弟弟 Erling 买了一个有趣的拼图。这是一个 $3 \times 3$ 的棋盘,上面有八个方形棋子,你可以将棋子滑入空格中。在随机打乱棋子后,游戏的目标是将棋盘从起始状态:

通过一次滑动一个棋子的方式,恢复到以下目标状态:

玩了一会儿拼图后,Erling 声称他可以用最少的步数解决任何实例。因为你不相信他,所以你编写了一个程序来最优地解决这些拼图。

第一行输入给出一个整数 $1 \le n \le 100$,表示测试用例的数量,随后是一个空行。每个测试用例由三行组成,给出了棋盘的起始配置,每行包含三个符号,随后是一个空行。所有测试用例都包含符号 $1 \dots 8$ 和 # 各一次,其中 # 代表空格。

对于每个测试用例,输出解决该拼图所需的最少移动次数,如果无法完成,则输出 impossible

样例

输入格式 1

2

123
4#5
786

123
456
87#

输出格式 1

2
impossible

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