我应该如何使用 maximumBy 和 compare 来实现我的功能？

Question

我必须在 Haskell 中进行 LZW 压缩，但我在搜索最长前缀时有点卡住了，因为我必须结合使用 maximumBy 和 compare 函数.

函数签名应如下所示：

longest :: [(Int, String)] -> (Int, String)

以下是描述要求的一些测试：

test_longest =
  [ longest [(30, "a"), (20, "abc"), (15, "ab")]  == (20, "abc")
  , longest [(30, "a"), (20, "abc"), (15, "abc")] == (15, "abc")
  ]

如有任何帮助，我们将不胜感激。

我在试图理解这个问题时想到的是：

longest (x:xs) = maximumBy (compare (length) x) xs

但肯定有问题。

Answer 1

这是将要执行的操作：

import Data.List

compareEntry :: (Int, [Char]) -> (Int, [Char]) -> Ordering
compareEntry (i1, s1) (i2, s2)
    | len1 > len2 = GT   -- First compare the length of the strings
    | len1 < len2 = LT
    | i1 < i2 = GT       -- If they are equal, compare the indices
    | i2 > i1 = LT       -- (mind the reversed order, since you want the lowest index)
    | otherwise = EQ
    where 
        len1 = length s1
        len2 = length s2

longest = maximumBy compareEntry

它可以写得更短但可读性较差。

Answer 2

@Eugene Sh 的解决方案的较短版本：

import Data.List
import Data.Ord

longest = maximumBy (comparing (length . snd) <> flip (comparing fst))

我应该如何使用 maximumBy 和 compare 来实现我的功能？

How should I use maximumBy and compare to implement my function?

haskell

compare