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  1. import qualified Data.Array
  2. import Data.Word
  3. import Data.List
  4. import Data.Array.ST
  5. import Data.Array.MArray
  6. import Control.Monad.ST
  7. import Control.Monad
  8. import Data.Array.IArray
  9.  
  10. upperbound = 1000000
  11.  
  12. collatz_array_mutable =
  13.   runSTUArray ( do
  14.     arr <- newArray (1, upperbound) maxBound :: ST s (STUArray s Word64 Word16)
  15.     writeArray arr 1 0
  16.     forM_ [1..upperbound] (\i -> 
  17.       do
  18.         {
  19.           let
  20.             next_i i = f ((if (even i) then i else 3 * i + 1) `div` 2)
  21.             f i = 
  22.               do
  23.                 if i > upperbound
  24.                  then
  25.                   do
  26.                     new_elem <- next_i i
  27.                     return (new_elem + 1)
  28.                  else
  29.                   do
  30.                     elem <- readArray arr i
  31.                     if elem == maxBound
  32.                      then
  33.                       do
  34.                         new_elem <- next_i i
  35.                         writeArray arr i (new_elem + 1)
  36.                         return (new_elem + 1)
  37.                      else
  38.                       return elem
  39.           in
  40.             f i
  41.         }
  42.       )
  43.     return arr
  44.   )
  45.  
  46. main = 
  47.   putStrLn $ show $ 
  48.     foldl1' (\(x1,x2) (y1,y2) -> if (x2 >= y2) then (x1, x2) else (y1, y2)) $! (assocs collatz_array_mutable)
  49.  
Success #stdin #stdout 0.74s 5680KB
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https://ideone.com/2M2ww
language:
Haskell (ghc 8.4.4)
created:
12 years ago
visibility:
public

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