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99 questions/Solutions/25

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Uses the solution for the previous problem. Choosing N distinct elements from a list of length N will yield a permutation.
 
Uses the solution for the previous problem. Choosing N distinct elements from a list of length N will yield a permutation.
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Or we can generate the permutation recursively:
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<haskell>
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import System.Random (randomRIO)
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rnd_permu :: [a] -> IO [a]
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rnd_permu [] = return []
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rnd_permu (x:xs) = do
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rand <- randomRIO (0, (length xs))
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rest <- rnd_permu xs
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return $ let (ys,zs) = splitAt rand rest
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in ys++(x:zs)
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</haskell>

Revision as of 06:24, 25 November 2010

Generate a random permutation of the elements of a list.

rnd_permu xs = diff_select' (length xs) xs

Uses the solution for the previous problem. Choosing N distinct elements from a list of length N will yield a permutation.

Or we can generate the permutation recursively:

import System.Random (randomRIO)
 
rnd_permu :: [a] -> IO [a]
rnd_permu []     = return []
rnd_permu (x:xs) = do
    rand <- randomRIO (0, (length xs))
    rest <- rnd_permu xs
    return $ let (ys,zs) = splitAt rand rest
             in ys++(x:zs)