31 lines
708 B
Haskell
31 lines
708 B
Haskell
-- The Fibonacci sequence is defined by the recurrence relation:
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--
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-- Fn = Fn−1 + Fn−2, where F1 = 1 and F2 = 1.
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-- Hence the first 12 terms will be:
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-- F1 = 1
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-- F2 = 1
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-- F3 = 2
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-- F4 = 3
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-- F5 = 5
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-- F6 = 8
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-- F7 = 13
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-- F8 = 21
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-- F9 = 34
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-- F10 = 55
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-- F11 = 89
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-- F12 = 144
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--
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-- The 12th term, F12, is the first term to contain three digits.
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--
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-- What is the index of the first term in the Fibonacci sequence to contain 1000 digits?
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fibs :: [Integer]
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fibs = 0:1:zipWith (+) fibs (tail fibs)
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thousandDigitFib = length $ takeWhile (\x -> length (show x) < 1000) fibs
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main = do
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let result = thousandDigitFib
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putStrLn $ "Project Euler, Problem 25\n"
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++ "Answer: " ++ show result
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