[Haskell-beginners] Project Euler #01 on HackerRank, Performance issue‏

[Animesh Saxena]

why not just use infinite series. mathematically...

series 1 = Mutiples of 3 
series 2 = Multiples of 5
Apply filter and sum to get the answer

-Animesh
On Jan 27, 2015, at 04:43 PM, Jean Lopes <hawu.bnu at gmail.com> wrote:

> Your solution runs really quick! I'll study it. Thank you
>
> 2015-01-27 22:25 GMT-02:00 Lyndon Maydwell <maydwell at gmail.com>:
>
>     Ah sorry, I didn't notice that you were doing that. The effectiveness of the trick really only comes into play though if you use an analytic solution for finding the sum of the multiples of 3, etc.
>
>     I haven't tested this code in a while, but here's what I wrote some time ago:
>
>
>     sum2 :: Integer -> Integer -> Integer -> Integer
>     sum2 a b ceiling = aX + bX - abX
>     where
>     aX  = sum1 a ceiling
>     bX  = sum1 b ceiling
>     abX = sum1 (a * b) ceiling
>
>     sum1 :: Integer -> Integer -> Integer
>     sum1 x ceiling = sum1' (even times) times x
>     where
>     times = ceiling `div` x
>
>     sum1' :: Bool -> Integer -> Integer -> Integer
>     sum1' True times x = area
>     where
>     area = (times + 1) * (times * x) `div` 2
>
>     sum1' False times x = max + area'
>     where
>     max   = times * x
>     area' = sum1' True (times - 1) x
>
>
>     Please excuse the poor Haskell style as it is quite possibly the first Haskell program I ever wrote.
>
>
>
>     On Wed, Jan 28, 2015 at 11:15 AM, Jean Lopes <hawu.bnu at gmail.com> wrote:
>
>         Thats actually what I did...
>
>         2015-01-27 22:11 GMT-02:00 Lyndon Maydwell <maydwell at gmail.com>:
>
>             I remember that when I had a look at Euler 1 I found that there's a fun solution that should run in "constant" time.
>
>             You can find the sum of the multiples of 3, add the multiples of 5, and then subtract the multiples of 3*5.
>
>             Is that the kind of thing you're looking for?
>
>              - Lyndon
>
>
>             On Wed, Jan 28, 2015 at 10:57 AM, Jean Lopes <hawu.bnu at gmail.com> wrote:
>
>                 I'm not really good at math, maybe I am missing something obvious ?
>                 Maybe some pointers as of where to start studying math in order to avoid this brute force attempts, at least to help in this particular problem
>
>                 2015-01-27 21:38 GMT-02:00 Brandon Allbery <allbery.b at gmail.com>:
>
>                     On Tue, Jan 27, 2015 at 6:29 PM, Jean Lopes <hawu.bnu at gmail.com> wrote:
>
>                         The problem to be solved: https://www.hackerrank.com/contests/projecteuler/challenges/euler001 
>
>
>                     It's worth remembering that the Euler problems are all about math understanding; often they are designed such that brute force solutions will time out or otherwise fail.
>
>                     -- 
>                     brandon s allbery kf8nh                               sine nomine associates
>                     allbery.b at gmail.com                                  ballbery at sinenomine.net
>                      
>                     unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
>                      
>
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