Project Euler 1: Multiples of 3 and 5 Solution

1// O(N)
2const solution = () => {
3  const N = 1000
4  let res = 0
5  for (let i = 1; i < N; i++) {
6    if (i % 3 === 0 || i % 5 === 0) {
7      res += i
8    }
9  }
10  console.log(res)
11}
12
13// O(1)
14// Ref for formular: https://math.stackexchange.com/a/9305
15const solution2 = () => {
16  const N = 1000
17
18  const sumDivisibleBy = x => {
19    const n = Math.floor((N - 1) / x)
20    return (x * (n * (n + 1))) / 2
21  }
22
23  const res = sumDivisibleBy(3) + sumDivisibleBy(5) - sumDivisibleBy(15)
24
25  console.log(res)
26}
27
28solution()
29solution2()