Wondering if anyone else has a solution for the 1st problem on the online course. The python program that finds the first 1000 prime numbers. I have a solution but apparently it is not very efficient because it is taking forever to run.

Question

Wondering if anyone else has a solution for the 1st problem on the online course.  The python program that finds the first 1000 prime numbers.  I have a solution but apparently it is not very efficient because it is taking forever to run.

anonymous · Answer

Try this http://mathworld.wolfram.com/SieveofEratosthenes.html

anonymous · Answer

There are a bunch of efficient algorithms out there for generating prime nums, such as the Sieve of Eratosthenes, but for the first 6.00 assignment even simply caching primes you've already found would be very quick

anonymous · Answer

trial division + caching* would be fast enough.... for tiny primes like 7919 even trial division without caching is good enough :-D

anonymous · Answer

http://rosettacode.org/wiki/Sieve_of_Eratosthenes#Python

anonymous · Answer

I programmed it to look for factors whos product was the number I was testing.  The test started out true unless it found the two factors.  That worked fine for the 1st 100 primes or so, but the 'trues per second' seem to be on the wrong end of an retricemptote approaching 0. lol

anonymous · Answer

only check for factors till sqrt(n)

anonymous · Answer

Great. If you like, you can post the code on a site like http://ideone.com and we can take a look at it.

anonymous · Answer

Maybe.  I doubt it's impressive.  This is the first program I've ever written.

anonymous · Answer

Took me a long time, too...

anonymous · Answer

That's okay; the first time I tried out 6.00, it took me ages to get used to it.

anonymous · Answer

Turns out I hadn't watched the lecture that spelled this out yet.  Light bulbs!!!  I redid it and it runs in about 10 seconds now.  I learned a lot messing around though.