Question

我是haskell的新手，我目前正在网格游戏中编写单词搜索，可以在对角线，行和列中找到单词。我使用Data.List.transpose来创建列，但输出总是创建新的空字符串。我尝试了过滤功能，但它没有改变输出：filter (not.null) (L.transpose y)。输出如下所示：["IYYPPOLFHTNMTDI"," ","UTVCGNVAEEZXEIR"," ","PDCPLTRUGSWTSQC"," ","GZEGUDGHSZTGSDT"," ","RMCEDJABPEUERTL"," ","ATTRVRXGKBRAMRA"," ","DZISDRASHAODEOP"," ","EVWWUWIXWBHGMMT"," ","ENAGCDYTYIOAOTO"," ","PRLCFFFEPDIVRKP"," ","EXZRNOKLOKPLYSO"," ","QSRESYZICYKUOLX"]

初始网格：

grid :: [String]
grid
     = ["I U P G R A D E E P E Q",
        "Y T D Z M T Z V N R X S",
        "Y V C E C T I W A L Z R",
        "P C P G E R S W G C R E",
        "P G L U D V D U C F N S",
        "O N T D J R R W D F O Y",
        "L V R G A X A I Y F K Z",
        "F A U H B G S X T E L I",
        "H E G S P K H W Y P O C",
        "T E S Z E B A B I D K Y",
        "N Z W T U R O H O I P K",
        "M X T G E A D G A V L U",
        "T E S S R M E M O R Y O",
        "D I Q D T R O M T K S L",
        "I R C T L A P T O P O X" ]

如何解决此问题或是否有更好的方法来转置字符串列表？

Answer 1

问题在于transpose将字符串视为字符列表，包括空格。如果你尝试过：

transpose ["ABC",
           "DE ",
           "FGH"]

你得到：

["ADF",
 "BEG",
 "C H"]

你可以看到包含的所有字符，空格都是转置的。

对于您的特定情况，可以轻松解决问题。您可以使用words和unwords将"A B C"转换为["A","B","C"]，然后在转置前后转换回来：

> import Data.List
> (map unwords . transpose . map words) ["A B C","D E F","G H I"]
["A D G","B E H","C F I"]
>

filter无法正常工作的原因是只有空字符串null - 一串空格非空。你可以使用：

> import Data.Char
> filter (not . all isSpace) ["abc","   ","def"]
["abc","def"]
>

作为旁注，您可能需要重新考虑是否要在程序内部用空格表示网格。看起来使用它们会更容易：

[["a","b","c"],["d","e","f"],["g","h","i"]]   :: [[String]]

或：

["abc","def","ghi"]   :: [[Char]]

内部，只在输入或输出网格时添加或减去空格。

对于前一种表示形式，您可以使用map words和map unwords来回转换。对于后者，您可以使用：

> map (intersperse ' ') ["abc","def","ghi"]
["a b c","d e f","g h i"]
> map (concat . words) ["a b c","d e f","g h i"]
["abc","def","ghi"]
>

使用空字符串转置返回列表

1 个答案: