From 6b16d921543a62d880171791d39bcc58560785fa Mon Sep 17 00:00:00 2001 From: Charles Date: Sun, 11 Aug 2019 22:36:40 +0200 Subject: haskell problems 001 -> 006 --- haskell/002-even_fibonacci_numbers.hs | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) create mode 100644 haskell/002-even_fibonacci_numbers.hs (limited to 'haskell/002-even_fibonacci_numbers.hs') diff --git a/haskell/002-even_fibonacci_numbers.hs b/haskell/002-even_fibonacci_numbers.hs new file mode 100644 index 0000000..ff5de91 --- /dev/null +++ b/haskell/002-even_fibonacci_numbers.hs @@ -0,0 +1,26 @@ +-- Even Fibonacci numbers + +-- Problem 2 +-- Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be: + +-- 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... + +-- By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms. + + +main = do + print (sum (filter even (fib_until 4000000))) + +fib_until threshold = fib_from_index_until 0 threshold + +fib_from_index_until :: Int -> Int -> [Int] +fib_from_index_until i threshold + | fib_i < threshold = fib_i:(fib_from_index_until (i + 1) threshold) + | otherwise = [] + where fib_i = fibonacci i + +fibonacci :: Int -> Int +fibonacci 0 = 0 +fibonacci 1 = 1 +fibonacci 2 = 1 +fibonacci x = fibonacci (x - 1) + fibonacci (x - 2) -- cgit