I thought it would be fun to create a thread where the community could solve a problem from Project Euler. This is Problem #1:
If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.
Look forward to seeing solutions in your language of choice!
Top comments (40)
I'll take a mathematical approach.
The sum of the first n positive integers is n*(n + 1)/2. Multiply by k, and you get the sum of the first n multiples of k.
There are 333 multiples of 3 below 1000, and 199 multiples of 5, so we get 166833 and 99500, respectively. But we can't just sum them, as we'd count the multiples of 15 twice (15 is their least common multiple), so we have to subtract those once (total: 33165).
Result: 233168
In general, let's use JavaScript for example:
There, no iterations, pure math π And blazing fast β‘
Using JavaScript's new support of
BigInt
, it's immediate even with huge numbers like 123456789012345678901234567890: it's 3556368375755728575115582031196717989244271707186887161545.This is very clever and very nice!
yesss the Gaussian sum is such a good tool!
I did this in LOLCODE (first program that I'm writing with it, probably not the best implementation)
πππππ
You can try it here
Answer in C# using LINQ.
Explanation
Enumerable.Range
generates a number between 1 & 1000Where
filters records that matches a condition (It's likefilter
in JS)Sum
is a convenience method for summing up a sequence (instead of doingAggregate((acc, n) => acc + n))
, which is equivalent toreduce
in JS)Source & Tests on Github.
short AND legible!
Thanks Joe :)
Ruby
JavaScript
It's a shame getting a range and a sum isn't quite as easy in JS.
Or generate the range with the es6 spread operator:
There's also a nasty (but shorter)
eval
hack to use in place of reduce. You can use.join(+)
to convert the array into a string containing each number joined by the '+' sign, then evaluate that string as if it's a JavaScript expression to get the sum:It's a bad practice to use eval, of course, but useful for JS code golf.
Or with lodash:
Here it is Β―\_(γ)_/Β―
I'm looking forward for feedbacks
Smallest nitpicking ever: declare
i
inside thefor
loop.It will prevent it from leaking outside the loop.
I wouldn't even call that nitpicking, that is solid best practice advice to avoid memory leaks.
Python
For fun: A shorter solution.
Great solution. Since I lost touch of python it was a little difficult. Now I understand.
Rubyβ¨πβ¨
In Java
Python
or Python One-Liner
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