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{- Copyright (c) 2020 JEON Myoungjin <jeongoon@g... > -}
module Combinations
( combinations
) where
combinations :: [a] -> Int -> [[a]]
combinations [] _ = []
combinations (m:ms) 1 = [m] : (combinations ms 1)
combinations [_] 2 = []
combinations [e,f] 2 = [[e,f]]
combinations (m:ms) 2 = sequence [[m], ms] ++ (combinations ms 2)
combinations mls n =
case totalLen `compare` n of
LT -> []
EQ -> [mls]
_ -> [ let leaders = map (fst) tups
in leaders ++ followers |
tups <- combinations (zip mls [0 .. room]) n',
let skipCount = ((snd.last) tups) + 1,
followers <- (combinations (drop skipCount mls) 2) ]
where
totalLen = length mls
room = totalLen - 2
n' = n - 2
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