Project Euler Problem #3 - Largest Prime Factor (in Java)

Either use my PrimeFactorization class that I wrote here (the largest factor in the prime factorization result), or use just the necessary component of it (below) to find the largest prime factor. 

  1. import java.math.BigInteger;

  3. /**
  4.   * The prime factors of 13195 are 5, 7, 13 and 29.
  5.   * What is the largest prime factor of the number 600851475143 ?
  6.   */

  8. public class Problem_3_Largest_Prime_Factor {

  10.   public static void main(String[] args) {
  11.     System.out.println(findLargestPrimeFactor(600851475143L));
  12.     System.out.println(findLargestBigPrimeFactor(new BigInteger("600851475143")));
  13.   }

  15.   /**
  16.     * Returns the largest prime factor of n.
  17.     */
  18.   public static long findLargestPrimeFactor(long n) {
  19.     long primeFactor = 1L;
  20.     long i = 2L;

  22.     while (i <= n / i) {
  23.       if (n % i == 0) {
  24.         primeFactor = i;
  25.         n /= i;
  26.       } else {
  27.         i++;
  28.       }
  29.     }

  31.     if (primeFactor < n) primeFactor = n;

  33.     return primeFactor;
  34.   }

  36.   /**
  37.     * Returns the largest prime factor of n.
  38.     */
  39.   public static BigInteger findLargestBigPrimeFactor(BigInteger n) {
  40.     BigInteger primeFactor = BigInteger.ONE;
  41.     BigInteger i = new BigInteger("2");
  42.   
  43.     while (i.compareTo(n.divide(i)) <= 0) {
  44.       if (n.mod(i).longValue() == 0) {
  45.         primeFactor = i;
  46.         n = n.divide(i);
  47.       } else {
  48.         i = i.add(BigInteger.ONE);
  49.       }
  50.     }

  52.     if (primeFactor.compareTo(n) < 0) primeFactor = n;

  54.     return primeFactor;
  55.   }
  56. }
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         Created: May 11, 2014
    Last Updated: May 10, 2020
Completed in full by: Michael Yaworski