Merge branch 'master' of https://github.com/manwar/perlweeklychallenge-club

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diff --git a/challenge-083/jeongoon/haskell/Combinations.hs b/challenge-083/jeongoon/haskell/Combinations.hs
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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 = sequence [ [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 (mls!!) ids
+            in  leaders ++ followers |
+            ids <- combinations [ 0 .. room ] n',
+            let skipCount = (last ids) + 1,
+                followers <- (combinations (drop skipCount mls) 2) ]
+  where
+    totalLen    = length mls
+    room        = totalLen - 2
+    n'          = n - 2