# Project Euler problem 10

rajarshi roy

Greenhorn

Posts: 21

posted 6 years ago

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

Can anyone please help me out???

Can anyone please help me out???

posted 6 years ago

You'll probably overflow the long. Try it with BigInteger.

"Any fool can write code that a computer can understand. Good programmers write code that humans can understand." --- Martin Fowler

Please correct my English.

Ulf Dittmer

Rancher

Posts: 42967

73

posted 6 years ago

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.

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.

Mike Simmons

Ranch Hand

Posts: 3036

10

posted 6 years ago

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.

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.

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.

posted 6 years ago

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

-Hunter

-Hunter

"If the facts don't fit the theory, get new facts" --Albert Einstein