31 lines
957 B
Haskell
31 lines
957 B
Haskell
-- n=5 max=5 -> 12345
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-- n=5 max=6 -> 12346, 12356, 12456, 13456, 23456
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-- n=5 max=7 -> 12347, 12357, 12367, 12457, 12467...
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-- n=1 max=1 -> 1
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-- n=1 max=2 -> 2
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-- n=1 max=3 -> 3
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--
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-- n=2 max=2 -> 12
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-- n=2 max=3 -> 13, 23
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-- n=2 max=4 -> 14, 24, 34
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-- n=2 max=5 -> 15, 26, 35, 45
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--
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-- n=3 max=3 -> 123
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-- n=3 max=4 -> 124, 134, 234
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-- n=3 max=5 -> 125, 135, 235, 145, 245, 345 (n=2,max=2 ; n=2,max=3 ; n=2,max=4)++[5]
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combination :: (Ord a) => Int -> a -> [a] -> [[a]]
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combination 0 max list = []
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combination n max (x:xs@(y:ys))
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| x>max = []
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| n==1 &&
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x<=max && y>max = [[x]]
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| otherwise = ( map (\z -> x:z) $ combination (n-1) max xs )
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++ combination n max xs
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all_combinations n xs = foldr (++) [] $ map (\i -> combination n (xs!!i) xs) [(n-1)..]
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main = do
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putStrLn $ show $ combination 5 5 [1..]
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mapM_ putStrLn (map show $ take 50 $ all_combinations 5 [1,3..])
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