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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	public static void main (String[] args) throws java.lang.Exception
  11. 	{
  12. 		System.out.println(nthPrime(25));
  13. 	}
  14.  
  15. 	public static int nthPrime(int n) {
  16.     if (n < 2) return 2;
  17.     if (n == 2) return 3;
  18.     int limit, root, count = 1;
  19.     limit = (int)(n*(Math.log(n) + Math.log(Math.log(n)))) + 3;
  20.     root = (int)Math.sqrt(limit) + 1;
  21.     limit = (limit-1)/2;
  22.     root = root/2 - 1;
  23.     boolean[] sieve = new boolean[limit];
  24.     for(int i = 0; i < root; ++i) {
  25.         if (!sieve[i]) {
  26.             ++count;
  27.             for(int j = 2*i*(i+3)+3, p = 2*i+3; j < limit; j += p) {
  28.                 sieve[j] = true;
  29.             }
  30.         }
  31.     }
  32.     int p;
  33.     for(p = root; count < n; ++p) {
  34.         if (!sieve[p]) {
  35.             ++count;
  36.         }
  37.     }
  38.     return 2*p+1;
  39. }
  40. }
Success #stdin #stdout 0.1s 320256KB
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https://ideone.com/neORk0
language:
Java (HotSpot 12)
created:
10 years ago
visibility:
public

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