Get 10001st prime number - Java Algorithm

Java examples for Algorithm:Number

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Description

Get 10001st prime number

Demo Code

/*/*  w ww  . j a v a 2  s . c o  m*/
 * By listing the first six prime numbers: 2, 3, 5, 7, 11, 
 * and 13, we can see that the 6th prime is 13.What is the 
 * 10 001st prime number?
 */
package number;

import java.util.ArrayList;

public class The10001stPrime {
  private static boolean isPrime(long n){
    if(n < 2)
      return false;
    else if(n == 2)
      return true;
    else if(n%2 == 0)
      return false;
    else{
      for(long i = 2; i <= java.lang.Math.sqrt(n); i++)
        if(n%i == 0)
          return false;
      return true;
    }
  }
  public static int nthPrime(int n){
    ArrayList<Integer> arr = new ArrayList<Integer>();
    for(int i = 2; arr.size() <= 10001; i++){
      if(isPrime(i))
        arr.add(i);
    }
    return (int) arr.get(n-1);
  }
  public static void main(String[] args) {
    System.out.println(nthPrime(10001));
  }
}

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