Question

我试图在haskell中解决Problem 11 of Project Euler。我几乎做到了，但是现在我卡住了，我想将表示为[String]的Matrix转换为表示为[[Int]]的矩阵。

我“绘制”了矩阵：

我想要的是什么：

"08 02 22 97 38 15 00 40                  [ ["08","02","22","97","38","15","00","40"],                [[08,02,22,97,38,15,00,40]
 49 49 99 40 17 81 18 57  map words lines   ["49","49","99","40","17","81","18","57"],      ??a        [49,49,99,40,17,81,18,57]
 81 49 31 73 55 79 14 29  ---------->       ["81","49","31","73","55","79","14","29"],  --------->     [81,49,31,73,55,79,14,29]
 52 70 95 23 04 60 11 42                    ["52","70","95","23","04","60","11","42"],                 [52,70,95,23,04,60,11,42]
 22 31 16 71 51 67 63 89                    ["22","31","16","71","51","67","63","89"],                 [22,31,16,71,51,67,63,89]
 24 47 32 60 99 03 45 02"                   ["24","47","32","60","99","03","45","02"] ]                [24,47,32,60,99,03,45,02]]

我坚持做最后的转换（?? a）

为了好奇（和学习），我也想知道如何做一个数字矩阵：

输入：

"123456789               [ "123456789"                    [ [1,2,3,4,5,6,7,8,9]
 124834924    lines        "124834924"         ??b          [1,2,4,8,3,4,9,2,4]
 328423423  --------->     "328423423"      --------->      [3,2,8,4,2,3,4,2,3]
 334243423                 "334243423"                      [3,3,4,2,4,3,4,2,3]
 932402343"                "932402343" ]                    [9,3,2,4,0,2,3,4,3] ]

制作（?? a）和（?? b）的最佳方法是什么？

Answer 1

你想要的是read功能：

read :: (Read a) => String -> a

这会仔细地将字符串解析为您期望的任何内容（只要它是类Read的实例，但幸运的是Int就是这样。）

所以只需在单词上映射，就像这样：

parseMatrix :: (Read a) => String -> [[a]]
parseMatrix s = map (map read . words) $ lines s

只需在期望[[Int]]的上下文中使用它，Haskell的类型推断将从那里获取它。

要获取数字，请记住String实际上只是[Char]。而不是使用words，映射一个函数，将每个Char转换为单个元素列表;其他一切都是一样的。

Haskell怀疑：如何将表示为：[String]的Matrix转换为表示为[[Int]]的Matrix？

1 个答案: