Monday, May 11, 2009

Groovy Prime Numbers

The other day I wanted to prove the power of Groovy to a few more core Java developers. I sat down and played with a little script that I think proves the power, or ease of use, of Groovy while having fun with number theory. My goal was to have a Collection that contains Prime Numbers calculated from a given range of numbers x to y, or in Groovy syntax x..y. I am taking a few things for granted with this script. For example, I know that 2 is the lowest Prime Number (it helps simplify the algorithm) and that 1 is not a Prime Number. So here's the script:

def t = 1..100
def v = []

t.each { n ->
    (2..n).each { d ->
        if(n % d == 0 && n != d)
        v.add(n)
    }
}

println t - v - 1

We have our range of numbers t and we are capturing the non-Prime numbers and adding them to our Collection v. The final line of the script is doing a lot of groovy work for us that would take a few more lines of code with plain Java syntax. What is it doing for us? It is taking our range of numbers t and subtracting (removing) our non-Prime numbers collected in v. This line is also removing the number 1 because we know that 1 is not a Prime Number. Finally, it is printing the result like so:

[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

Very cool stuff. Now, I know that many of us are rarely building a Collection of Prime Numbers and I know this script does not do things in a timely manner with a range like 1..10000 (it took a couple of minutes), but I am sure this feature of Collections in Groovy can be utilized in many ways in my development.