programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other all forums
this forum made possible by our volunteer staff, including ...
Marshals:
• Campbell Ritchie
• Ron McLeod
• Paul Clapham
• Bear Bibeault
• Junilu Lacar
Sheriffs:
• Jeanne Boyarsky
• Tim Cooke
• Henry Wong
Saloon Keepers:
• Tim Moores
• Stephan van Hulst
• Tim Holloway
• salvin francis
• Frits Walraven
Bartenders:
• Scott Selikoff
• Piet Souris
• Carey Brown

# Project Euler problem 10

Greenhorn
Posts: 21
I was trying to solve problem 10 of Project Euler .I wrote a code ,but it does not work for higher values.

Bartender
Posts: 2700
You'll probably overflow the long. Try it with BigInteger.

Rancher
Posts: 43016
76
What do you mean by "higher values" - higher than 2000000? I think even an "int" should work fine for all involved fields for the original problem.

If you start with "boolean b = true", then you don't need the "if (i == num)" block. One should avoid accessing loop variables outside of the "for" block.

Rancher
Posts: 3625
40

rajarshi roy wrote:I wrote a code ,but it does not work for higher values.

In what way does it not work? Do you get the wrong answer? Does it throw an exception? Does it take an unacceptably long time to finish?

Looking at your code, I suspect it's the latter. It's going to take a long time to check all those values to see if they're prime. To find is a value n is prime, do you really have to loop through every number less than n? There are a couple of huge improvements you can make on this method that will make it much faster.

Wouter Oet wrote:You'll probably overflow the long. Try it with BigInteger.

I'm pretty sure this problem can be done without BigInteger. All the primes are less than 2 million, and there are much less than 2 million of them, so their sum should be much less than 2 million times 2 million, which is 4 trillion. That should fit easily inside a long.

Ranch Hand
Posts: 492
You should look up something called the Sieve of Eratosthenes. It is a really quick way to test if a number is prime.

-Hunter

rajarshi roy
Greenhorn
Posts: 21
the code works fine for smaller values,say below 100000.But it takes exceptionally long time to finish for values like 1000000.I will try to change the code.Thanks for your advices.

 Sunglasses. AKA Coolness prosthetic. This tiny ad doesn't need shades: Thread Boost feature https://coderanch.com/t/674455/Thread-Boost-feature