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largest-series-product corner cases #89

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Merged
merged 3 commits into from
Feb 21, 2016
Merged

largest-series-product corner cases #89

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5a1730a
largest-series-product: Nothing for too small input
petertseng Jan 23, 2016
545af93
largest-series-product: Test for zero span, nonempty string
petertseng Jan 23, 2016
cee0dde
largest-series-product: Add a case where all spans contain 0
petertseng Jan 23, 2016
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6 changes: 3 additions & 3 deletions largest-series-product/example.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@ slices :: Integral a => Int -> String -> [[a]]
slices n = go . digits
where go xs = map (take n) $ take (length xs - pred n) (tails xs)

largestProduct :: Integral a => Int -> String -> a
largestProduct :: Integral a => Int -> String -> Maybe a
largestProduct n text = case map product (slices n text) of
[] -> 1
products -> maximum products
[] -> Nothing
products -> Just $ maximum products
15 changes: 10 additions & 5 deletions largest-series-product/largest-series-product_test.hs
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Expand Up @@ -18,8 +18,11 @@ main = exitProperly $ runTestTT $ TestList
ints :: [Int] -> [Int]
ints = id

int :: Int -> Int
int = id
int :: Int -> Maybe Int
int = Just

intNothing :: Maybe Int
intNothing = Nothing

seriesTests :: [Test]
seriesTests = map TestCase
Expand All @@ -43,8 +46,10 @@ seriesTests = map TestCase
, int 28350 @=?
largestProduct 6 "52677741234314237566414902593461595376319419139427"
, int 1 @=? largestProduct 0 ""
-- unlike the Ruby implementation, no error is expected for too small input
, int 1 @=? largestProduct 4 "123"
-- edge case :)
, int 1 @=? largestProduct 0 "123"
, intNothing @=? largestProduct 1 ""
, intNothing @=? largestProduct 4 "123"
-- if all spans contain zero, result is zero.
, int 0 @=? largestProduct 3 "99099"
, int 0 @=? largestProduct 2 "00"
]