2. Sieve of Eratosthenes #

Created Tuesday 28 July 2020

1. We write all the numbers in a bool array.
2. All are true initially.
3. We start from 2, mark all its multiples as false.
4. Then continue for the rest till √n i.e highest factor.

Tweaks:

1. As we go to multiples, we can start from the current one i.e start from i*i
2. We can skip a number if number % is multiple of any of the previous numbers. Skip 4 because 2 is already over.
3. We go till √n, and not till n. Everything has been covered.