Upside-down numbers: Difference between revisions
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=={{header|Haskell}}==
<syntaxhighlight lang="Haskell">import Data.Char ( digitToInt )
import Data.List ( unfoldr , (!!) )
findLimits :: (Int , Int) -> [(Int , Int)]
findLimits (st , end ) = unfoldr(\(x , y ) -> if x > y then Nothing else
Just ((x , y ) , (x + 1 , y - 1 ))) (st , end )
isUpsideDown :: Int -> Bool
isUpsideDown n
|elem '0' str = False
|otherwise = all (\(a , b ) -> digitToInt( str !! a ) + digitToInt ( str !!
b ) == 10 ) $ findLimits ( 0 , length str - 1 )
where
str = show n
main :: IO ( )
main = do
let upsideDowns = take 5000 $ filter isUpsideDown [1..]
putStrLn "The first fifty upside-down numbers!"
print $ take 50 upsideDowns
putStr "The five hundredth such number : "
print $ upsideDowns !! 499
putStr "The five thousandth such number : "
print $ last upsideDowns</syntaxhighlight>
{{out}}
<pre>
The first fifty upside-down numbers!
[5,19,28,37,46,55,64,73,82,91,159,258,357,456,555,654,753,852,951,1199,1289,1379,1469,1559,1649,1739,1829,1919,2198,2288,2378,2468,2558,2648,2738,2828,2918,3197,3287,3377,3467,3557,3647,3737,3827,3917,4196,4286,4376,4466]
The five hundredth such number : 494616
The five thousandth such number : 56546545
</pre>
=={{header|jq}}==
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