Project Euler: Problem 9

A Pythagorean triplet is a set of three natural numbers, for which,

$a < b < c \qquad a^2 + b^2 = c^2$

For example,

There exists exactly one Pythagorean triplet for which,

Find the product abc.

Solution

This I wasn’t quite sure how to solve effectively and my solution is probably not the fastest or most clever, but at least it is pretty simple To start off, we need a source of Pythagorean triplets.

public class PythagoreanTriples
: IEnumerable<Triple<ulong, ulong, ulong>>
{
public IEnumerator<Triple<ulong, ulong, ulong>> GetEnumerator()
{
for (ulong c = 1;; c++)
for (ulong b = 1; b <= c; b++)
for (ulong a = 1; a < b; a++)
if ((a*a) + (b*b) == c*c)
yield return Tuple.From(a, b, c);
}

IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}

Note: You can find the Triple class in the Lokad Shared Libraries.

And that’s pretty much what we need to solve this problem actually.

var t = new PythagoreanTriples()
.First(x => x.Item1 + x.Item2 + x.Item3 == 1000);
var answer = t.Item1 * t.Item2 * t.Item3;

This piece of code simply goes through triplets until it finds the first one fulfilling our requirement. It runs in around 230 milliseconds, which is acceptable enough.

Do you have a more clever way to do this? Please leave a comment and share