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transfer, lol it worked 1st time?

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This commit is contained in:
Aaro Koivukangas
2025-12-22 19:55:50 +02:00
parent 76f5ecf036
commit 6378f45fea
1 changed files with 11 additions and 1 deletions
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exercises/Set4a.hs
+11 -1
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@@ -233,7 +233,17 @@ freqs (x:xs) = foldr updateFreq (Map.singleton x 1) xs
-- ==> fromList [("Bob",100),("Mike",50)] -- ==> fromList [("Bob",100),("Mike",50)]
transfer :: String -> String -> Int -> Map.Map String Int -> Map.Map String Int transfer :: String -> String -> Int -> Map.Map String Int -> Map.Map String Int
transfer from to amount bank = todo transfer from to amount bank | Map.notMember from bank = bank
| Map.notMember to bank = bank
| amount < 0 = bank
| (Map.findWithDefault 0 from bank) - amount < 0 = bank
| otherwise = Map.alter (apply (-) amount) from (Map.alter (apply (+) amount) to bank)
where
apply :: (Int -> Int -> Int) -> Int -> Maybe Int -> Maybe Int
apply op amount value = case value of
Nothing -> Just $ 0 `op` amount
Just value -> Just $ value `op` amount
------------------------------------------------------------------------------ ------------------------------------------------------------------------------
-- Ex 11: given an Array and two indices, swap the elements in the indices. -- Ex 11: given an Array and two indices, swap the elements in the indices.