trjhtr

Question:

Find the sum of multiples of 3 or 5 up to 1000

I have come up with this solution that is bit more generic than the first 1000 per se:

let multiplesSum = n => 

 let sum = 0

 for (let i = 0; i < n; i++) 
 return sum

Instead of pushing everything to an array use a variable and sum the numbers as they are looping.

Implementation

Your implementation is clean, robust and easy to understand. I suggest only small changes:

• Declare multiplesSum as const to prevent accidental rebinding / overriding later on.


• 
  multiplesSum(n) should compute the sum of multiples of 3 or 5 up to and including n. Sum formulas are usually following this convention.


• I prefer terminating statements with semicolons instead of relying on JavaScript's automatic semicolon insertion.

Algorithm

Your algorithm is simple and easy to understand, but comes with a linear runtime complexity of O(n).

An algorithm with constant runtime complexity O(1) exists. Here are some pointers in case you are stuck:

• Given a positive integer n, how often do 3 or 5 fit into n? Division and Math.floor give the answer.


• Arithmetic sequences such as 3 + 6 + 9 + ... have simple, explicit sum formulas.


• By adding (3 + 6 + 9 + ...) + (5 + 10 + 15 + ...), you count some numbers twice, so you need to find and subtract those.