3 votes

Consider a 3-puzzle where, like in the usual 8-puzzle game, a tile can only move to an adjacent empty space. Given the initial state

1 | 2 |

3 |

which of the following state cannot be reached?

A | 3 | 1 |

2 |

B | 3 | |

2 | 1 |

C | 1 | 3 |

2 |

D | 2 | |

1 | 3 |