The Project Euler thread

[Reincarnate]

Not every problem can be done with pencil and paper.

[leonid]

Rubix sent me to solve this

A bit of paperwork and then lots of wolframalpha

[Reincarnate]

Nicely done

[stargroup100]

sorry I should've been more clear

I was referring to problem nine specifically, involving pythagorean triples

[rushyrulz]

brute forcing 12 and it's not going so well. I'm almost an hour in and still no solution.

The sequence of triangle numbers is generated by adding the natural numbers. 
So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be:

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

Let us list the factors of the first seven triangle numbers:

 1: 1
 3: 1,3
 6: 1,2,3,6
10: 1,2,5,10
15: 1,3,5,15
21: 1,3,7,21
28: 1,2,4,7,14,28
We can see that 28 is the first triangle number to have over five divisors.

What is the value of the first triangle number to have over five hundred divisors?

In hindsight, I probably would have used a much more efficient factor breakdown algorithm had I known it would take this long.

[Reincarnate]

using brute force = not very interesting

usually more fun to try for the faster approaches

[rushyrulz]

I'm sure there's a very elegant mathematical solution for all of these, but I'm just trying to get as far as I can :P

[stargroup100]

I did the first 30 (excluding 12) and even a couple of the 300+ ones before I figured out 12. I don't know why but that one was hard for me

[rushyrulz]

Probably since there are so many different things you need to account for in 12. Not only do you need a gigantic 500+ factor number, but it also needs to be a summation of n number which is tricky to check for.

[Guest15937]

My brute force of 12 took 15 seconds to run.

[beary605]

does project euler ever teach you algorithms, e.x. dynamic programming, breadth/depth first search

[rushyrulz]

Project Euler doesn't directly 'teach' you anything.

[beary605]

Originally Posted by rushyrulz

Project Euler doesn't directly 'teach' you anything.

rephrasing question then

does project euler ever REQUIRE you to know algorithms, e.x. dynamic programming, breadth/depth first search

[rushyrulz]

It's basically algorithm development, and if dynamic programming, breadth/depth first search is required for efficiency sake, then yes.

Also, rewrote my factorization algorithm and I solved 12 in 5 seconds :P

[Reincarnate]

Originally Posted by beary605

does project euler ever teach you algorithms, e.x. dynamic programming, breadth/depth first search

absolutely

even more so once you start venturing into the harder stages (where the problems also become much more interesting)

DP, especially, is used quite often

[Reincarnate]

For example, try your hand at any of these:



http://projecteuler.net/problem=161
http://projecteuler.net/problem=425
http://projecteuler.net/problem=442

[Reincarnate]

And of course, (some) of the big kahunas that will require both mathematical and programmatical sorcery:

http://projecteuler.net/problem=289
http://projecteuler.net/problem=328
http://projecteuler.net/problem=344
http://projecteuler.net/problem=361
http://projecteuler.net/problem=415

[rushyrulz]

you almost have to be too smart...

[stargroup100]

ohhhh the eulerian circle one looks cool

really tempted to try that one lol

[beary605]

ohoho this will be fun, i should get back to project euler