• Egiht(八种方法)


    Problem Description

    The 15-puzzle has been around for over 100 years; even if you don't know it by that name, you've seen it. It is constructed with 15 sliding tiles, each with a number from 1 to 15 on it, and all packed into a 4 by 4 frame with one tile missing. Let's call the missing tile 'x'; the object of the puzzle is to arrange the tiles so that they are ordered as:

    1 2 3 4
    5 6 7 8
    9 10 11 12
    13 14 15 x

    where the only legal operation is to exchange 'x' with one of the tiles with which it shares an edge. As an example, the following sequence of moves solves a slightly scrambled puzzle:

    1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
    5 6 7 8 5 6 7 8 5 6 7 8 5 6 7 8
    9 x 10 12 9 10 x 12 9 10 11 12 9 10 11 12
    13 14 11 15 13 14 11 15 13 14 x 15 13 14 15 x
    r-> d-> r->

    The letters in the previous row indicate which neighbor of the 'x' tile is swapped with the 'x' tile at each step; legal values are 'r','l','u' and 'd', for right, left, up, and down, respectively.

    Not all puzzles can be solved; in 1870, a man named Sam Loyd was famous for distributing an unsolvable version of the puzzle, and
    frustrating many people. In fact, all you have to do to make a regular puzzle into an unsolvable one is to swap two tiles (not counting the missing 'x' tile, of course).

    In this problem, you will write a program for solving the less well-known 8-puzzle, composed of tiles on a three by three
    arrangement.

    Input

    You will receive, several descriptions of configuration of the 8 puzzle. One description is just a list of the tiles in their initial positions, with the rows listed from top to bottom, and the tiles listed from left to right within a row, where the tiles are represented by numbers 1 to 8, plus 'x'. For example, this puzzle

    1 2 3
    x 4 6
    7 5 8

    is described by this list:

    1 2 3 x 4 6 7 5 8

    Output

    You will print to standard output either the word ``unsolvable'', if the puzzle has no solution, or a string consisting entirely of the letters 'r', 'l', 'u' and 'd' that describes a series of moves that produce a solution. The string should include no spaces and start at the beginning of the line. Do not print a blank line between cases.

    SampleInput

    2  3  4  1  5  x  7  6  8

    SampleOutput

    ullddrurdllurdruldr
    就是给你一个序列,然后要你通过四种移动方式,回到最初的序列,输出答案,题目有SPJ,无需输出最优方法。
    这道题可谓是搜索中的精髓了,最开始我就是一个简单的双向搜索,结果TLE了,看了网上的博客加了剪枝之后过了。
    但是后来和队友聊这题,发现这道题的解题思路不止一种,队友说有八种

    然后找到一篇博客,里面一共讲了八种解法,应该是很全面的。
    博客链接:https://www.cnblogs.com/zufezzt/p/5659276.html
    至于我的代码就没什么好讲的了,确实用双向BFS加剪枝可以AC这道题,但这道题的精髓远远不在于此,也见识到了自己的学识浅薄。我也道不出个所以然,所以这道题我就不详细讲了。

    还是那句话以梦为马,不负韶华。
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  • 原文地址:https://www.cnblogs.com/xenny/p/9404645.html
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