Java Program to find largest prime factor of a number

JavaObject Oriented ProgrammingProgramming

Following is the Java code to find the largest prime factor of a number −

Example

 Live Demo

import java.io.*;
import java.util.*;
public class Demo{
   static long maxPrimeFactors( long val){
      long max_prime = -1;
      while (val % 2 == 0) {
         max_prime = 2;
         val >>= 1;
      }
      for (int i = 3; i <= Math.sqrt(val); i += 2){
         while (val % i == 0){
            max_prime = i;
            val = val / i;
         }
      }
      if (val > 2)
      max_prime = val;
      return max_prime;
   }
   public static void main(String[] args){
      int val = 148592;
      System.out.println("The largest prime factor of 148592 is ");
      System.out.println(maxPrimeFactors(val));
      val = 890654;
      System.out.println("The largest prime factor of 890654 is ");
      System.out.println(maxPrimeFactors(val));
   }
}

Output

The largest prime factor of 148592 is
251
The largest prime factor of 890654 is
4591

A class named Demo contains a static function that tales a value, and a ‘while’ condition is defined, which checks whether the value modulus 2 is 0. If it is 0, then, a variable (max_prime) is assigned the value 2. Otherwise, it is right bit shifted by 1. Again, a ‘for’ loop is iterated over elements from 3 to square root of the value, and incremented by 2 after every iteration.

Now, a ‘while’ loop checks if the value modulus iterator is 0. If yes, a variable (max_prime) is assigned the value that is currently being iterated. The value is divided by the iterated value. If this value is greater than 2, then this value (max_prime) is assigned to a variable named max_prime. This is returned. In the main function, an integer value is defined and the largest prime factor is found out by calling the function with the specific argument.

raja
Published on 04-Jul-2020 13:28:57
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