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SieveOfEratosthenes.java
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74 lines (63 loc) · 1.72 KB
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public class SieveOfEratosthenes {
private static int limit = 1000; // Only used if no value passed through.
private static boolean[] booleanArray;
private static int totalPrimes;
private static long calcTime;
public static void main(String[] args)
{
long startTime = System.currentTimeMillis();
setup(args);
findAllPrimes();
displayPrimes();
long endTime = System.currentTimeMillis();
long timeTaken = endTime - startTime;
System.out.println();
System.out.println();
System.out.println("It took " + calcTime + "ms to calculate the prime numbers below " + limit + ".");
System.out.println("The complete algorithm took " + timeTaken + "ms to finish.");
System.out.println();
System.out.println();
System.out.println("There are " + totalPrimes + " prime numbers below " + limit + ".");
}
private static void setup(String[] args)
{
if(args.length > 0)
{
limit = Integer.parseInt(args[0]);
}
booleanArray = new boolean[limit + 1];
for(int position = 0; position <= limit; position++)
{
booleanArray[position] = false;
}
}
private static void findAllPrimes()
{
long calcStartTime = System.currentTimeMillis();
for(int position = 2; position <= Math.sqrt(limit); position++)
{
if(booleanArray[position] == false)
{
int multiple = position * 2;
while(multiple <= limit)
{
booleanArray[multiple] = true;
multiple += position;
}
}
}
long calcEndTime = System.currentTimeMillis();
calcTime = calcEndTime - calcStartTime;
}
private static void displayPrimes()
{
for(int position = 2; position <= limit; position++)
{
if(booleanArray[position] == false)
{
totalPrimes++;
System.out.print(position + ", ");
}
}
}
}