Hi!
I've come across this piece of code of a (modified?) sieve and I'm trying to figure out what sieve[i]
means and how it works, specially the 2nd for.
Would you help me, please?
Thanks!
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sieve[i]
gives you the index of the biggest prime factor. The index is one-based.sieve[20] == 3
, because20 = 2*2*5
andprimes[3] == 5
(5
is the third prime number)Using this method, you generate the prime factorization pretty quick. You can find the biggest prime number using the
sieve
, divide by this number and repeat with the result.I think you meant
prime[5] = 3
, right?No,
primes
is a list of primes.primes = { 0, 2, 3, 5, 7, 11, ... }
Ah, sorry I totally misunderstood.
I thought you meant to give another example, which is
sieve[5] = 3
, and didn't notice the difference in arrays' names. Sorry about that :D