?? sieve.java
字號:
/**
* @version 1.20 1999-07-03
* @author Cay Horstmann
*/
import java.util.*;
public class Sieve
{ public static final boolean PRINT = false;
public static void main(String[] s)
{ int n = 1000000;
long start = System.currentTimeMillis();
BitSet b = new BitSet(n);
int count = 0;
int i;
for (i = 2; i <= n; i++)
b.set(i);
i = 2;
while (i * i <= n)
{ if (b.get(i))
{ if (PRINT) System.out.println(i);
count++;
int k = 2 * i;
while (k <= n)
{ b.clear(k);
k += i;
}
}
i++;
}
while (i <= n)
{ if (b.get(i))
{ if (PRINT) System.out.println(i);
count++;
}
i++;
}
long end = System.currentTimeMillis();
System.out.println(count + " primes");
System.out.println((end - start) + " milliseconds");
}
}
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