Palindrome dates: Difference between revisions
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=={{header|Haskell}}== |
=={{header|Haskell}}== |
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<syntaxhighlight lang="haskell">import Data. |
<syntaxhighlight lang="haskell">import Data.List (unfoldr) |
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import Data.List.Split (chunksOf) |
import Data.List.Split (chunksOf) |
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import Data.Tuple (swap) |
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import Data.Bool (bool) |
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import Data.Maybe (mapMaybe) |
import Data.Maybe (mapMaybe) |
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import Data.Time.Calendar (Day, fromGregorianValid) |
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-------------------- PALINDROMIC DATES ------------------- |
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palinDates :: [Day] |
palinDates :: [Day] |
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palinDay y = fromGregorianValid y m d |
palinDay y = fromGregorianValid y m d |
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where |
where |
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[m, d] = unDigits <$> chunksOf 2 |
[m, d] = unDigits <$> chunksOf 2 |
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unfoldr ((flip bool Nothing . Just . swap . flip quotRem 10) <*> (0 ==)) |
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--------------------------- TEST ------------------------- |
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main :: IO () |
main :: IO () |
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main = |
main = |
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let n = length palinDates |
let n = length palinDates |
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putStrLn |
in putStrLn ("Count of palindromic dates [2021..9999]: " |
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<> show n) >> |
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putStrLn "\nFirst 15:" |
putStrLn "\nFirst 15:" >> |
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mapM_ print |
mapM_ print (take 15 palinDates) >> |
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putStrLn "\nLast 15:" |
putStrLn "\nLast 15:" >> |
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mapM_ print |
mapM_ print (take 15 (drop (n - 15) palinDates)) |
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------------------------- GENERIC ------------------------ |
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reversedDecimalDigits = unfoldr go |
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where |
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go n |
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| 0 < n = Just $ swap (quotRem n 10) |
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| otherwise = Nothing |
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{{Out}} |
{{Out}} |
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<pre>Count of palindromic dates [2021..9999]: 284 |
<pre>Count of palindromic dates [2021..9999]: 284 |