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- {-
- You are given the following information, but you may prefer to do some research for yourself.
- 1 Jan 1900 was a Monday.
- Thirty days has September,
- April, June and November.
- All the rest have thirty-one, Saving February alone,
- Which has twenty-eight, rain or shine.
- And on leap years, twenty-nine.
- A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
- How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
- -}
- import Utils
- solution :: Int
- solution = go' sD (iterate weekdayNext (weekdayOfDate sD)) 0
- where
- sD = Date 1901 1 1
- eD = Date 2000 12 31
- go' :: Date -> [Weekday] -> Int -> Int
- go' d (x:xs) c
- | d == eD = c
- | otherwise = go' (dateNextDay d) xs (if (x == Sunday && (dateDay d) == 1) then (c+1) else c)
- main :: IO ()
- main = putStrLn ("Solution: " ++ show solution)
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