P3610 [USACO17JAN]Cow Navigation奶牛导航

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    • 75提交
  • 题目提供者FarmerJohn2
  • 标签 USACO 2017
  • 难度 普及+/提高
  • 时空限制 1s / 128MB

题解

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    题目描述

    Bessie has gotten herself stuck on the wrong side of Farmer John's barn again, and since her vision is so poor, she needs your help navigating across the barn.

    The barn is described by an $N \times N$ grid of square cells ($2 \leq N \leq 20$), some being empty and some containing impassable haybales. Bessie starts in the lower-left corner (cell 1,1) and wants to move to the upper-right corner (cell $N,N$). You can guide her by telling her a sequence of instructions, each of which is either "forward", "turn left 90 degrees", or "turn right 90 degrees". You want to issue the shortest sequence of instructions that will guide her to her destination. If you instruct Bessie to move off the grid (i.e., into the barn wall) or into a haybale, she will not move and will skip to the next command in your sequence.

    Unfortunately, Bessie doesn't know if she starts out facing up (towards cell 1,2) or right (towards cell 2,1). You need to give the shortest sequence of directions that will guide her to the goal regardless of which case is true. Once she reaches the goal she will ignore further commands.

    贝西误把自己困在了FJ谷仓的一侧。因为她的视力很差,她在脱困时需要你的帮助。

    谷仓的平面图由一个方形细胞图(即所画图)呈现,有些细胞(即单位)是空的,其他的则是不可通过的柴草堆。贝西从左下角开始(细胞1,1)想一路搬到右上角。你可以引导她,告诉她一个指令序列,指令可以为“前进”“左转90度”“右转90度”。你需要得出能够使她到达目的地所用的最短指令序列。如果你指示贝西离开谷仓或至柴草堆,她不会移动,会直接跳到下一个命令序列。

    不幸的是,贝西不知道她一开始所朝的方向(可能是上或右),而序列无需考虑这种情况,只需到达目标即可。(最后一句的正确性待考证)

    输入输出格式

    输入格式:

    The first line of input contains $N$.

    Each of the $N$ following lines contains a string of exactly $N$ characters, representing the barn. The first character of the last line is cell 1,1. The last character of the first line is cell N, N.

    Each character will either be an H to represent a haybale or an E to represent an empty square.

    It is guaranteed that cells 1,1 and $N,N$ will be empty, and furthermore it is guaranteed that there is a path of empty squares from cell 1,1 to cell $N, N$.

    输出格式:

    On a single line of output, output the length of the shortest sequence of directions that will guide Bessie to the goal, irrespective whether she starts facing up or right.

    输入输出样例

    输入样例#1: 复制
    3
    EHE
    EEE
    EEE
    输出样例#1: 复制
    9

    说明

    感谢 @lzyzz250 的翻译

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