Nth Prime

calculatePrime.java

/* Returns the nth prime number - uses the Sieve of Eratosthenes */
public int calculatePrime(int limit, int n) {
	List<Integer> working_set = new ArrayList<Integer>();
	int p=2;
	
	// Fill our working set with consecutive integers (longs) from 2 through n
	System.out.println("Populating working set...");
	for(int i=2; i<=limit; i++)
		working_set.add(i);
	
	System.out.println("Finding primes...");
	// The working set will shrink until hopefully it contains only primes
	for(int i=0; i<working_set.size(); i++) {			
		// Enumerate multiples of p and mark them (in our case, just remove them)
		for(int j=p; j<working_set.size(); j++) {
			int current=working_set.get(j);
			if(current%p == 0) { // current is a multiple of p
				working_set.remove(j); // "Mark" this number - i.e. remove from our working set
				j--;
			}
		}
		
		p=working_set.get(i);
		System.out.println(p);
	}
	
	if(n<=working_set.size())
		return working_set.get(n-1);
	else
		return -1*working_set.size(); // If there aren't that many primes, return the size of the working set
}